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3196 lines
88 KiB
3196 lines
88 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* Memory merging support. |
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* |
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* This code enables dynamic sharing of identical pages found in different |
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* memory areas, even if they are not shared by fork() |
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* |
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* Copyright (C) 2008-2009 Red Hat, Inc. |
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* Authors: |
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* Izik Eidus |
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* Andrea Arcangeli |
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* Chris Wright |
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* Hugh Dickins |
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*/ |
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|
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#include <linux/errno.h> |
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#include <linux/mm.h> |
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#include <linux/fs.h> |
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#include <linux/mman.h> |
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#include <linux/sched.h> |
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#include <linux/sched/mm.h> |
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#include <linux/sched/coredump.h> |
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#include <linux/rwsem.h> |
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#include <linux/pagemap.h> |
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#include <linux/rmap.h> |
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#include <linux/spinlock.h> |
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#include <linux/xxhash.h> |
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#include <linux/delay.h> |
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#include <linux/kthread.h> |
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#include <linux/wait.h> |
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#include <linux/slab.h> |
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#include <linux/rbtree.h> |
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#include <linux/memory.h> |
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#include <linux/mmu_notifier.h> |
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#include <linux/swap.h> |
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#include <linux/ksm.h> |
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#include <linux/hashtable.h> |
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#include <linux/freezer.h> |
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#include <linux/oom.h> |
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#include <linux/numa.h> |
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|
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#include <asm/tlbflush.h> |
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#include "internal.h" |
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|
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#ifdef CONFIG_NUMA |
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#define NUMA(x) (x) |
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#define DO_NUMA(x) do { (x); } while (0) |
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#else |
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#define NUMA(x) (0) |
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#define DO_NUMA(x) do { } while (0) |
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#endif |
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|
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/** |
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* DOC: Overview |
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* |
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* A few notes about the KSM scanning process, |
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* to make it easier to understand the data structures below: |
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* |
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* In order to reduce excessive scanning, KSM sorts the memory pages by their |
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* contents into a data structure that holds pointers to the pages' locations. |
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* |
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* Since the contents of the pages may change at any moment, KSM cannot just |
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* insert the pages into a normal sorted tree and expect it to find anything. |
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* Therefore KSM uses two data structures - the stable and the unstable tree. |
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* |
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* The stable tree holds pointers to all the merged pages (ksm pages), sorted |
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* by their contents. Because each such page is write-protected, searching on |
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* this tree is fully assured to be working (except when pages are unmapped), |
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* and therefore this tree is called the stable tree. |
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* |
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* The stable tree node includes information required for reverse |
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* mapping from a KSM page to virtual addresses that map this page. |
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* |
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* In order to avoid large latencies of the rmap walks on KSM pages, |
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* KSM maintains two types of nodes in the stable tree: |
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* |
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* * the regular nodes that keep the reverse mapping structures in a |
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* linked list |
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* * the "chains" that link nodes ("dups") that represent the same |
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* write protected memory content, but each "dup" corresponds to a |
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* different KSM page copy of that content |
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* |
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* Internally, the regular nodes, "dups" and "chains" are represented |
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* using the same struct stable_node structure. |
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* |
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* In addition to the stable tree, KSM uses a second data structure called the |
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* unstable tree: this tree holds pointers to pages which have been found to |
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* be "unchanged for a period of time". The unstable tree sorts these pages |
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* by their contents, but since they are not write-protected, KSM cannot rely |
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* upon the unstable tree to work correctly - the unstable tree is liable to |
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* be corrupted as its contents are modified, and so it is called unstable. |
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* |
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* KSM solves this problem by several techniques: |
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* |
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* 1) The unstable tree is flushed every time KSM completes scanning all |
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* memory areas, and then the tree is rebuilt again from the beginning. |
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* 2) KSM will only insert into the unstable tree, pages whose hash value |
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* has not changed since the previous scan of all memory areas. |
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* 3) The unstable tree is a RedBlack Tree - so its balancing is based on the |
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* colors of the nodes and not on their contents, assuring that even when |
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* the tree gets "corrupted" it won't get out of balance, so scanning time |
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* remains the same (also, searching and inserting nodes in an rbtree uses |
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* the same algorithm, so we have no overhead when we flush and rebuild). |
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* 4) KSM never flushes the stable tree, which means that even if it were to |
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* take 10 attempts to find a page in the unstable tree, once it is found, |
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* it is secured in the stable tree. (When we scan a new page, we first |
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* compare it against the stable tree, and then against the unstable tree.) |
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* |
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* If the merge_across_nodes tunable is unset, then KSM maintains multiple |
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* stable trees and multiple unstable trees: one of each for each NUMA node. |
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*/ |
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|
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/** |
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* struct mm_slot - ksm information per mm that is being scanned |
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* @link: link to the mm_slots hash list |
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* @mm_list: link into the mm_slots list, rooted in ksm_mm_head |
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* @rmap_list: head for this mm_slot's singly-linked list of rmap_items |
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* @mm: the mm that this information is valid for |
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*/ |
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struct mm_slot { |
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struct hlist_node link; |
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struct list_head mm_list; |
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struct rmap_item *rmap_list; |
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struct mm_struct *mm; |
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}; |
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|
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/** |
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* struct ksm_scan - cursor for scanning |
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* @mm_slot: the current mm_slot we are scanning |
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* @address: the next address inside that to be scanned |
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* @rmap_list: link to the next rmap to be scanned in the rmap_list |
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* @seqnr: count of completed full scans (needed when removing unstable node) |
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* |
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* There is only the one ksm_scan instance of this cursor structure. |
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*/ |
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struct ksm_scan { |
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struct mm_slot *mm_slot; |
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unsigned long address; |
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struct rmap_item **rmap_list; |
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unsigned long seqnr; |
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}; |
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|
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/** |
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* struct stable_node - node of the stable rbtree |
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* @node: rb node of this ksm page in the stable tree |
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* @head: (overlaying parent) &migrate_nodes indicates temporarily on that list |
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* @hlist_dup: linked into the stable_node->hlist with a stable_node chain |
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* @list: linked into migrate_nodes, pending placement in the proper node tree |
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* @hlist: hlist head of rmap_items using this ksm page |
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* @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid) |
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* @chain_prune_time: time of the last full garbage collection |
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* @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN |
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* @nid: NUMA node id of stable tree in which linked (may not match kpfn) |
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*/ |
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struct stable_node { |
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union { |
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struct rb_node node; /* when node of stable tree */ |
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struct { /* when listed for migration */ |
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struct list_head *head; |
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struct { |
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struct hlist_node hlist_dup; |
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struct list_head list; |
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}; |
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}; |
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}; |
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struct hlist_head hlist; |
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union { |
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unsigned long kpfn; |
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unsigned long chain_prune_time; |
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}; |
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/* |
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* STABLE_NODE_CHAIN can be any negative number in |
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* rmap_hlist_len negative range, but better not -1 to be able |
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* to reliably detect underflows. |
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*/ |
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#define STABLE_NODE_CHAIN -1024 |
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int rmap_hlist_len; |
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#ifdef CONFIG_NUMA |
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int nid; |
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#endif |
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}; |
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|
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/** |
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* struct rmap_item - reverse mapping item for virtual addresses |
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* @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list |
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* @anon_vma: pointer to anon_vma for this mm,address, when in stable tree |
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* @nid: NUMA node id of unstable tree in which linked (may not match page) |
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* @mm: the memory structure this rmap_item is pointing into |
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* @address: the virtual address this rmap_item tracks (+ flags in low bits) |
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* @oldchecksum: previous checksum of the page at that virtual address |
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* @node: rb node of this rmap_item in the unstable tree |
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* @head: pointer to stable_node heading this list in the stable tree |
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* @hlist: link into hlist of rmap_items hanging off that stable_node |
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*/ |
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struct rmap_item { |
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struct rmap_item *rmap_list; |
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union { |
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struct anon_vma *anon_vma; /* when stable */ |
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#ifdef CONFIG_NUMA |
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int nid; /* when node of unstable tree */ |
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#endif |
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}; |
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struct mm_struct *mm; |
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unsigned long address; /* + low bits used for flags below */ |
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unsigned int oldchecksum; /* when unstable */ |
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union { |
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struct rb_node node; /* when node of unstable tree */ |
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struct { /* when listed from stable tree */ |
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struct stable_node *head; |
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struct hlist_node hlist; |
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}; |
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}; |
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}; |
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|
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#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */ |
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#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */ |
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#define STABLE_FLAG 0x200 /* is listed from the stable tree */ |
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|
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/* The stable and unstable tree heads */ |
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static struct rb_root one_stable_tree[1] = { RB_ROOT }; |
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static struct rb_root one_unstable_tree[1] = { RB_ROOT }; |
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static struct rb_root *root_stable_tree = one_stable_tree; |
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static struct rb_root *root_unstable_tree = one_unstable_tree; |
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|
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/* Recently migrated nodes of stable tree, pending proper placement */ |
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static LIST_HEAD(migrate_nodes); |
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#define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev) |
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|
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#define MM_SLOTS_HASH_BITS 10 |
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static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS); |
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static struct mm_slot ksm_mm_head = { |
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.mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list), |
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}; |
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static struct ksm_scan ksm_scan = { |
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.mm_slot = &ksm_mm_head, |
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}; |
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static struct kmem_cache *rmap_item_cache; |
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static struct kmem_cache *stable_node_cache; |
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static struct kmem_cache *mm_slot_cache; |
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/* The number of nodes in the stable tree */ |
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static unsigned long ksm_pages_shared; |
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|
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/* The number of page slots additionally sharing those nodes */ |
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static unsigned long ksm_pages_sharing; |
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|
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/* The number of nodes in the unstable tree */ |
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static unsigned long ksm_pages_unshared; |
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|
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/* The number of rmap_items in use: to calculate pages_volatile */ |
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static unsigned long ksm_rmap_items; |
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|
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/* The number of stable_node chains */ |
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static unsigned long ksm_stable_node_chains; |
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|
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/* The number of stable_node dups linked to the stable_node chains */ |
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static unsigned long ksm_stable_node_dups; |
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|
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/* Delay in pruning stale stable_node_dups in the stable_node_chains */ |
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static unsigned int ksm_stable_node_chains_prune_millisecs = 2000; |
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|
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/* Maximum number of page slots sharing a stable node */ |
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static int ksm_max_page_sharing = 256; |
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|
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/* Number of pages ksmd should scan in one batch */ |
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static unsigned int ksm_thread_pages_to_scan = 100; |
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/* Milliseconds ksmd should sleep between batches */ |
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static unsigned int ksm_thread_sleep_millisecs = 20; |
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/* Checksum of an empty (zeroed) page */ |
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static unsigned int zero_checksum __read_mostly; |
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|
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/* Whether to merge empty (zeroed) pages with actual zero pages */ |
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static bool ksm_use_zero_pages __read_mostly; |
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#ifdef CONFIG_NUMA |
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/* Zeroed when merging across nodes is not allowed */ |
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static unsigned int ksm_merge_across_nodes = 1; |
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static int ksm_nr_node_ids = 1; |
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#else |
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#define ksm_merge_across_nodes 1U |
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#define ksm_nr_node_ids 1 |
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#endif |
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#define KSM_RUN_STOP 0 |
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#define KSM_RUN_MERGE 1 |
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#define KSM_RUN_UNMERGE 2 |
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#define KSM_RUN_OFFLINE 4 |
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static unsigned long ksm_run = KSM_RUN_STOP; |
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static void wait_while_offlining(void); |
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static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait); |
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static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait); |
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static DEFINE_MUTEX(ksm_thread_mutex); |
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static DEFINE_SPINLOCK(ksm_mmlist_lock); |
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#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\ |
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sizeof(struct __struct), __alignof__(struct __struct),\ |
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(__flags), NULL) |
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static int __init ksm_slab_init(void) |
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{ |
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rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0); |
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if (!rmap_item_cache) |
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goto out; |
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stable_node_cache = KSM_KMEM_CACHE(stable_node, 0); |
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if (!stable_node_cache) |
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goto out_free1; |
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mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); |
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if (!mm_slot_cache) |
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goto out_free2; |
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return 0; |
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out_free2: |
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kmem_cache_destroy(stable_node_cache); |
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out_free1: |
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kmem_cache_destroy(rmap_item_cache); |
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out: |
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return -ENOMEM; |
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} |
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static void __init ksm_slab_free(void) |
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{ |
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kmem_cache_destroy(mm_slot_cache); |
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kmem_cache_destroy(stable_node_cache); |
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kmem_cache_destroy(rmap_item_cache); |
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mm_slot_cache = NULL; |
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} |
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static __always_inline bool is_stable_node_chain(struct stable_node *chain) |
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{ |
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return chain->rmap_hlist_len == STABLE_NODE_CHAIN; |
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} |
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static __always_inline bool is_stable_node_dup(struct stable_node *dup) |
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{ |
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return dup->head == STABLE_NODE_DUP_HEAD; |
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} |
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static inline void stable_node_chain_add_dup(struct stable_node *dup, |
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struct stable_node *chain) |
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{ |
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VM_BUG_ON(is_stable_node_dup(dup)); |
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dup->head = STABLE_NODE_DUP_HEAD; |
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VM_BUG_ON(!is_stable_node_chain(chain)); |
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hlist_add_head(&dup->hlist_dup, &chain->hlist); |
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ksm_stable_node_dups++; |
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} |
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|
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static inline void __stable_node_dup_del(struct stable_node *dup) |
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{ |
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VM_BUG_ON(!is_stable_node_dup(dup)); |
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hlist_del(&dup->hlist_dup); |
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ksm_stable_node_dups--; |
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} |
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static inline void stable_node_dup_del(struct stable_node *dup) |
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{ |
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VM_BUG_ON(is_stable_node_chain(dup)); |
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if (is_stable_node_dup(dup)) |
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__stable_node_dup_del(dup); |
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else |
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rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid)); |
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#ifdef CONFIG_DEBUG_VM |
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dup->head = NULL; |
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#endif |
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} |
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static inline struct rmap_item *alloc_rmap_item(void) |
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{ |
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struct rmap_item *rmap_item; |
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rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL | |
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__GFP_NORETRY | __GFP_NOWARN); |
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if (rmap_item) |
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ksm_rmap_items++; |
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return rmap_item; |
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} |
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static inline void free_rmap_item(struct rmap_item *rmap_item) |
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{ |
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ksm_rmap_items--; |
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rmap_item->mm = NULL; /* debug safety */ |
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kmem_cache_free(rmap_item_cache, rmap_item); |
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} |
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|
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static inline struct stable_node *alloc_stable_node(void) |
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{ |
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/* |
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* The allocation can take too long with GFP_KERNEL when memory is under |
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* pressure, which may lead to hung task warnings. Adding __GFP_HIGH |
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* grants access to memory reserves, helping to avoid this problem. |
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*/ |
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return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH); |
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} |
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static inline void free_stable_node(struct stable_node *stable_node) |
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{ |
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VM_BUG_ON(stable_node->rmap_hlist_len && |
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!is_stable_node_chain(stable_node)); |
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kmem_cache_free(stable_node_cache, stable_node); |
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} |
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|
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static inline struct mm_slot *alloc_mm_slot(void) |
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{ |
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if (!mm_slot_cache) /* initialization failed */ |
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return NULL; |
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return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); |
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} |
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static inline void free_mm_slot(struct mm_slot *mm_slot) |
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{ |
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kmem_cache_free(mm_slot_cache, mm_slot); |
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} |
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static struct mm_slot *get_mm_slot(struct mm_struct *mm) |
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{ |
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struct mm_slot *slot; |
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|
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hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm) |
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if (slot->mm == mm) |
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return slot; |
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|
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return NULL; |
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} |
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|
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static void insert_to_mm_slots_hash(struct mm_struct *mm, |
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struct mm_slot *mm_slot) |
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{ |
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mm_slot->mm = mm; |
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hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm); |
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} |
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|
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/* |
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* ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's |
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* page tables after it has passed through ksm_exit() - which, if necessary, |
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* takes mmap_lock briefly to serialize against them. ksm_exit() does not set |
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* a special flag: they can just back out as soon as mm_users goes to zero. |
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* ksm_test_exit() is used throughout to make this test for exit: in some |
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* places for correctness, in some places just to avoid unnecessary work. |
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*/ |
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static inline bool ksm_test_exit(struct mm_struct *mm) |
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{ |
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return atomic_read(&mm->mm_users) == 0; |
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} |
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|
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/* |
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* We use break_ksm to break COW on a ksm page: it's a stripped down |
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* |
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* if (get_user_pages(addr, 1, FOLL_WRITE, &page, NULL) == 1) |
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* put_page(page); |
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* |
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* but taking great care only to touch a ksm page, in a VM_MERGEABLE vma, |
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* in case the application has unmapped and remapped mm,addr meanwhile. |
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* Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP |
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* mmap of /dev/mem, where we would not want to touch it. |
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* |
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* FAULT_FLAG/FOLL_REMOTE are because we do this outside the context |
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* of the process that owns 'vma'. We also do not want to enforce |
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* protection keys here anyway. |
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*/ |
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static int break_ksm(struct vm_area_struct *vma, unsigned long addr) |
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{ |
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struct page *page; |
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vm_fault_t ret = 0; |
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|
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do { |
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cond_resched(); |
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page = follow_page(vma, addr, |
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FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE); |
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if (IS_ERR_OR_NULL(page)) |
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break; |
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if (PageKsm(page)) |
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ret = handle_mm_fault(vma, addr, |
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FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE, |
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NULL); |
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else |
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ret = VM_FAULT_WRITE; |
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put_page(page); |
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} while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM))); |
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/* |
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* We must loop because handle_mm_fault() may back out if there's |
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* any difficulty e.g. if pte accessed bit gets updated concurrently. |
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* |
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* VM_FAULT_WRITE is what we have been hoping for: it indicates that |
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* COW has been broken, even if the vma does not permit VM_WRITE; |
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* but note that a concurrent fault might break PageKsm for us. |
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* |
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* VM_FAULT_SIGBUS could occur if we race with truncation of the |
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* backing file, which also invalidates anonymous pages: that's |
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* okay, that truncation will have unmapped the PageKsm for us. |
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* |
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* VM_FAULT_OOM: at the time of writing (late July 2009), setting |
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* aside mem_cgroup limits, VM_FAULT_OOM would only be set if the |
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* current task has TIF_MEMDIE set, and will be OOM killed on return |
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* to user; and ksmd, having no mm, would never be chosen for that. |
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* |
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* But if the mm is in a limited mem_cgroup, then the fault may fail |
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* with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and |
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* even ksmd can fail in this way - though it's usually breaking ksm |
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* just to undo a merge it made a moment before, so unlikely to oom. |
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* |
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* That's a pity: we might therefore have more kernel pages allocated |
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* than we're counting as nodes in the stable tree; but ksm_do_scan |
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* will retry to break_cow on each pass, so should recover the page |
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* in due course. The important thing is to not let VM_MERGEABLE |
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* be cleared while any such pages might remain in the area. |
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*/ |
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return (ret & VM_FAULT_OOM) ? -ENOMEM : 0; |
|
} |
|
|
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static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm, |
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unsigned long addr) |
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{ |
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struct vm_area_struct *vma; |
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if (ksm_test_exit(mm)) |
|
return NULL; |
|
vma = vma_lookup(mm, addr); |
|
if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
|
return NULL; |
|
return vma; |
|
} |
|
|
|
static void break_cow(struct rmap_item *rmap_item) |
|
{ |
|
struct mm_struct *mm = rmap_item->mm; |
|
unsigned long addr = rmap_item->address; |
|
struct vm_area_struct *vma; |
|
|
|
/* |
|
* It is not an accident that whenever we want to break COW |
|
* to undo, we also need to drop a reference to the anon_vma. |
|
*/ |
|
put_anon_vma(rmap_item->anon_vma); |
|
|
|
mmap_read_lock(mm); |
|
vma = find_mergeable_vma(mm, addr); |
|
if (vma) |
|
break_ksm(vma, addr); |
|
mmap_read_unlock(mm); |
|
} |
|
|
|
static struct page *get_mergeable_page(struct rmap_item *rmap_item) |
|
{ |
|
struct mm_struct *mm = rmap_item->mm; |
|
unsigned long addr = rmap_item->address; |
|
struct vm_area_struct *vma; |
|
struct page *page; |
|
|
|
mmap_read_lock(mm); |
|
vma = find_mergeable_vma(mm, addr); |
|
if (!vma) |
|
goto out; |
|
|
|
page = follow_page(vma, addr, FOLL_GET); |
|
if (IS_ERR_OR_NULL(page)) |
|
goto out; |
|
if (PageAnon(page)) { |
|
flush_anon_page(vma, page, addr); |
|
flush_dcache_page(page); |
|
} else { |
|
put_page(page); |
|
out: |
|
page = NULL; |
|
} |
|
mmap_read_unlock(mm); |
|
return page; |
|
} |
|
|
|
/* |
|
* This helper is used for getting right index into array of tree roots. |
|
* When merge_across_nodes knob is set to 1, there are only two rb-trees for |
|
* stable and unstable pages from all nodes with roots in index 0. Otherwise, |
|
* every node has its own stable and unstable tree. |
|
*/ |
|
static inline int get_kpfn_nid(unsigned long kpfn) |
|
{ |
|
return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn)); |
|
} |
|
|
|
static struct stable_node *alloc_stable_node_chain(struct stable_node *dup, |
|
struct rb_root *root) |
|
{ |
|
struct stable_node *chain = alloc_stable_node(); |
|
VM_BUG_ON(is_stable_node_chain(dup)); |
|
if (likely(chain)) { |
|
INIT_HLIST_HEAD(&chain->hlist); |
|
chain->chain_prune_time = jiffies; |
|
chain->rmap_hlist_len = STABLE_NODE_CHAIN; |
|
#if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA) |
|
chain->nid = NUMA_NO_NODE; /* debug */ |
|
#endif |
|
ksm_stable_node_chains++; |
|
|
|
/* |
|
* Put the stable node chain in the first dimension of |
|
* the stable tree and at the same time remove the old |
|
* stable node. |
|
*/ |
|
rb_replace_node(&dup->node, &chain->node, root); |
|
|
|
/* |
|
* Move the old stable node to the second dimension |
|
* queued in the hlist_dup. The invariant is that all |
|
* dup stable_nodes in the chain->hlist point to pages |
|
* that are write protected and have the exact same |
|
* content. |
|
*/ |
|
stable_node_chain_add_dup(dup, chain); |
|
} |
|
return chain; |
|
} |
|
|
|
static inline void free_stable_node_chain(struct stable_node *chain, |
|
struct rb_root *root) |
|
{ |
|
rb_erase(&chain->node, root); |
|
free_stable_node(chain); |
|
ksm_stable_node_chains--; |
|
} |
|
|
|
static void remove_node_from_stable_tree(struct stable_node *stable_node) |
|
{ |
|
struct rmap_item *rmap_item; |
|
|
|
/* check it's not STABLE_NODE_CHAIN or negative */ |
|
BUG_ON(stable_node->rmap_hlist_len < 0); |
|
|
|
hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { |
|
if (rmap_item->hlist.next) |
|
ksm_pages_sharing--; |
|
else |
|
ksm_pages_shared--; |
|
VM_BUG_ON(stable_node->rmap_hlist_len <= 0); |
|
stable_node->rmap_hlist_len--; |
|
put_anon_vma(rmap_item->anon_vma); |
|
rmap_item->address &= PAGE_MASK; |
|
cond_resched(); |
|
} |
|
|
|
/* |
|
* We need the second aligned pointer of the migrate_nodes |
|
* list_head to stay clear from the rb_parent_color union |
|
* (aligned and different than any node) and also different |
|
* from &migrate_nodes. This will verify that future list.h changes |
|
* don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it. |
|
*/ |
|
BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes); |
|
BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1); |
|
|
|
if (stable_node->head == &migrate_nodes) |
|
list_del(&stable_node->list); |
|
else |
|
stable_node_dup_del(stable_node); |
|
free_stable_node(stable_node); |
|
} |
|
|
|
enum get_ksm_page_flags { |
|
GET_KSM_PAGE_NOLOCK, |
|
GET_KSM_PAGE_LOCK, |
|
GET_KSM_PAGE_TRYLOCK |
|
}; |
|
|
|
/* |
|
* get_ksm_page: checks if the page indicated by the stable node |
|
* is still its ksm page, despite having held no reference to it. |
|
* In which case we can trust the content of the page, and it |
|
* returns the gotten page; but if the page has now been zapped, |
|
* remove the stale node from the stable tree and return NULL. |
|
* But beware, the stable node's page might be being migrated. |
|
* |
|
* You would expect the stable_node to hold a reference to the ksm page. |
|
* But if it increments the page's count, swapping out has to wait for |
|
* ksmd to come around again before it can free the page, which may take |
|
* seconds or even minutes: much too unresponsive. So instead we use a |
|
* "keyhole reference": access to the ksm page from the stable node peeps |
|
* out through its keyhole to see if that page still holds the right key, |
|
* pointing back to this stable node. This relies on freeing a PageAnon |
|
* page to reset its page->mapping to NULL, and relies on no other use of |
|
* a page to put something that might look like our key in page->mapping. |
|
* is on its way to being freed; but it is an anomaly to bear in mind. |
|
*/ |
|
static struct page *get_ksm_page(struct stable_node *stable_node, |
|
enum get_ksm_page_flags flags) |
|
{ |
|
struct page *page; |
|
void *expected_mapping; |
|
unsigned long kpfn; |
|
|
|
expected_mapping = (void *)((unsigned long)stable_node | |
|
PAGE_MAPPING_KSM); |
|
again: |
|
kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */ |
|
page = pfn_to_page(kpfn); |
|
if (READ_ONCE(page->mapping) != expected_mapping) |
|
goto stale; |
|
|
|
/* |
|
* We cannot do anything with the page while its refcount is 0. |
|
* Usually 0 means free, or tail of a higher-order page: in which |
|
* case this node is no longer referenced, and should be freed; |
|
* however, it might mean that the page is under page_ref_freeze(). |
|
* The __remove_mapping() case is easy, again the node is now stale; |
|
* the same is in reuse_ksm_page() case; but if page is swapcache |
|
* in migrate_page_move_mapping(), it might still be our page, |
|
* in which case it's essential to keep the node. |
|
*/ |
|
while (!get_page_unless_zero(page)) { |
|
/* |
|
* Another check for page->mapping != expected_mapping would |
|
* work here too. We have chosen the !PageSwapCache test to |
|
* optimize the common case, when the page is or is about to |
|
* be freed: PageSwapCache is cleared (under spin_lock_irq) |
|
* in the ref_freeze section of __remove_mapping(); but Anon |
|
* page->mapping reset to NULL later, in free_pages_prepare(). |
|
*/ |
|
if (!PageSwapCache(page)) |
|
goto stale; |
|
cpu_relax(); |
|
} |
|
|
|
if (READ_ONCE(page->mapping) != expected_mapping) { |
|
put_page(page); |
|
goto stale; |
|
} |
|
|
|
if (flags == GET_KSM_PAGE_TRYLOCK) { |
|
if (!trylock_page(page)) { |
|
put_page(page); |
|
return ERR_PTR(-EBUSY); |
|
} |
|
} else if (flags == GET_KSM_PAGE_LOCK) |
|
lock_page(page); |
|
|
|
if (flags != GET_KSM_PAGE_NOLOCK) { |
|
if (READ_ONCE(page->mapping) != expected_mapping) { |
|
unlock_page(page); |
|
put_page(page); |
|
goto stale; |
|
} |
|
} |
|
return page; |
|
|
|
stale: |
|
/* |
|
* We come here from above when page->mapping or !PageSwapCache |
|
* suggests that the node is stale; but it might be under migration. |
|
* We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(), |
|
* before checking whether node->kpfn has been changed. |
|
*/ |
|
smp_rmb(); |
|
if (READ_ONCE(stable_node->kpfn) != kpfn) |
|
goto again; |
|
remove_node_from_stable_tree(stable_node); |
|
return NULL; |
|
} |
|
|
|
/* |
|
* Removing rmap_item from stable or unstable tree. |
|
* This function will clean the information from the stable/unstable tree. |
|
*/ |
|
static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) |
|
{ |
|
if (rmap_item->address & STABLE_FLAG) { |
|
struct stable_node *stable_node; |
|
struct page *page; |
|
|
|
stable_node = rmap_item->head; |
|
page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK); |
|
if (!page) |
|
goto out; |
|
|
|
hlist_del(&rmap_item->hlist); |
|
unlock_page(page); |
|
put_page(page); |
|
|
|
if (!hlist_empty(&stable_node->hlist)) |
|
ksm_pages_sharing--; |
|
else |
|
ksm_pages_shared--; |
|
VM_BUG_ON(stable_node->rmap_hlist_len <= 0); |
|
stable_node->rmap_hlist_len--; |
|
|
|
put_anon_vma(rmap_item->anon_vma); |
|
rmap_item->head = NULL; |
|
rmap_item->address &= PAGE_MASK; |
|
|
|
} else if (rmap_item->address & UNSTABLE_FLAG) { |
|
unsigned char age; |
|
/* |
|
* Usually ksmd can and must skip the rb_erase, because |
|
* root_unstable_tree was already reset to RB_ROOT. |
|
* But be careful when an mm is exiting: do the rb_erase |
|
* if this rmap_item was inserted by this scan, rather |
|
* than left over from before. |
|
*/ |
|
age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); |
|
BUG_ON(age > 1); |
|
if (!age) |
|
rb_erase(&rmap_item->node, |
|
root_unstable_tree + NUMA(rmap_item->nid)); |
|
ksm_pages_unshared--; |
|
rmap_item->address &= PAGE_MASK; |
|
} |
|
out: |
|
cond_resched(); /* we're called from many long loops */ |
|
} |
|
|
|
static void remove_trailing_rmap_items(struct rmap_item **rmap_list) |
|
{ |
|
while (*rmap_list) { |
|
struct rmap_item *rmap_item = *rmap_list; |
|
*rmap_list = rmap_item->rmap_list; |
|
remove_rmap_item_from_tree(rmap_item); |
|
free_rmap_item(rmap_item); |
|
} |
|
} |
|
|
|
/* |
|
* Though it's very tempting to unmerge rmap_items from stable tree rather |
|
* than check every pte of a given vma, the locking doesn't quite work for |
|
* that - an rmap_item is assigned to the stable tree after inserting ksm |
|
* page and upping mmap_lock. Nor does it fit with the way we skip dup'ing |
|
* rmap_items from parent to child at fork time (so as not to waste time |
|
* if exit comes before the next scan reaches it). |
|
* |
|
* Similarly, although we'd like to remove rmap_items (so updating counts |
|
* and freeing memory) when unmerging an area, it's easier to leave that |
|
* to the next pass of ksmd - consider, for example, how ksmd might be |
|
* in cmp_and_merge_page on one of the rmap_items we would be removing. |
|
*/ |
|
static int unmerge_ksm_pages(struct vm_area_struct *vma, |
|
unsigned long start, unsigned long end) |
|
{ |
|
unsigned long addr; |
|
int err = 0; |
|
|
|
for (addr = start; addr < end && !err; addr += PAGE_SIZE) { |
|
if (ksm_test_exit(vma->vm_mm)) |
|
break; |
|
if (signal_pending(current)) |
|
err = -ERESTARTSYS; |
|
else |
|
err = break_ksm(vma, addr); |
|
} |
|
return err; |
|
} |
|
|
|
static inline struct stable_node *page_stable_node(struct page *page) |
|
{ |
|
return PageKsm(page) ? page_rmapping(page) : NULL; |
|
} |
|
|
|
static inline void set_page_stable_node(struct page *page, |
|
struct stable_node *stable_node) |
|
{ |
|
page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM); |
|
} |
|
|
|
#ifdef CONFIG_SYSFS |
|
/* |
|
* Only called through the sysfs control interface: |
|
*/ |
|
static int remove_stable_node(struct stable_node *stable_node) |
|
{ |
|
struct page *page; |
|
int err; |
|
|
|
page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK); |
|
if (!page) { |
|
/* |
|
* get_ksm_page did remove_node_from_stable_tree itself. |
|
*/ |
|
return 0; |
|
} |
|
|
|
/* |
|
* Page could be still mapped if this races with __mmput() running in |
|
* between ksm_exit() and exit_mmap(). Just refuse to let |
|
* merge_across_nodes/max_page_sharing be switched. |
|
*/ |
|
err = -EBUSY; |
|
if (!page_mapped(page)) { |
|
/* |
|
* The stable node did not yet appear stale to get_ksm_page(), |
|
* since that allows for an unmapped ksm page to be recognized |
|
* right up until it is freed; but the node is safe to remove. |
|
* This page might be in a pagevec waiting to be freed, |
|
* or it might be PageSwapCache (perhaps under writeback), |
|
* or it might have been removed from swapcache a moment ago. |
|
*/ |
|
set_page_stable_node(page, NULL); |
|
remove_node_from_stable_tree(stable_node); |
|
err = 0; |
|
} |
|
|
|
unlock_page(page); |
|
put_page(page); |
|
return err; |
|
} |
|
|
|
static int remove_stable_node_chain(struct stable_node *stable_node, |
|
struct rb_root *root) |
|
{ |
|
struct stable_node *dup; |
|
struct hlist_node *hlist_safe; |
|
|
|
if (!is_stable_node_chain(stable_node)) { |
|
VM_BUG_ON(is_stable_node_dup(stable_node)); |
|
if (remove_stable_node(stable_node)) |
|
return true; |
|
else |
|
return false; |
|
} |
|
|
|
hlist_for_each_entry_safe(dup, hlist_safe, |
|
&stable_node->hlist, hlist_dup) { |
|
VM_BUG_ON(!is_stable_node_dup(dup)); |
|
if (remove_stable_node(dup)) |
|
return true; |
|
} |
|
BUG_ON(!hlist_empty(&stable_node->hlist)); |
|
free_stable_node_chain(stable_node, root); |
|
return false; |
|
} |
|
|
|
static int remove_all_stable_nodes(void) |
|
{ |
|
struct stable_node *stable_node, *next; |
|
int nid; |
|
int err = 0; |
|
|
|
for (nid = 0; nid < ksm_nr_node_ids; nid++) { |
|
while (root_stable_tree[nid].rb_node) { |
|
stable_node = rb_entry(root_stable_tree[nid].rb_node, |
|
struct stable_node, node); |
|
if (remove_stable_node_chain(stable_node, |
|
root_stable_tree + nid)) { |
|
err = -EBUSY; |
|
break; /* proceed to next nid */ |
|
} |
|
cond_resched(); |
|
} |
|
} |
|
list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) { |
|
if (remove_stable_node(stable_node)) |
|
err = -EBUSY; |
|
cond_resched(); |
|
} |
|
return err; |
|
} |
|
|
|
static int unmerge_and_remove_all_rmap_items(void) |
|
{ |
|
struct mm_slot *mm_slot; |
|
struct mm_struct *mm; |
|
struct vm_area_struct *vma; |
|
int err = 0; |
|
|
|
spin_lock(&ksm_mmlist_lock); |
|
ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next, |
|
struct mm_slot, mm_list); |
|
spin_unlock(&ksm_mmlist_lock); |
|
|
|
for (mm_slot = ksm_scan.mm_slot; |
|
mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) { |
|
mm = mm_slot->mm; |
|
mmap_read_lock(mm); |
|
for (vma = mm->mmap; vma; vma = vma->vm_next) { |
|
if (ksm_test_exit(mm)) |
|
break; |
|
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
|
continue; |
|
err = unmerge_ksm_pages(vma, |
|
vma->vm_start, vma->vm_end); |
|
if (err) |
|
goto error; |
|
} |
|
|
|
remove_trailing_rmap_items(&mm_slot->rmap_list); |
|
mmap_read_unlock(mm); |
|
|
|
spin_lock(&ksm_mmlist_lock); |
|
ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next, |
|
struct mm_slot, mm_list); |
|
if (ksm_test_exit(mm)) { |
|
hash_del(&mm_slot->link); |
|
list_del(&mm_slot->mm_list); |
|
spin_unlock(&ksm_mmlist_lock); |
|
|
|
free_mm_slot(mm_slot); |
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags); |
|
mmdrop(mm); |
|
} else |
|
spin_unlock(&ksm_mmlist_lock); |
|
} |
|
|
|
/* Clean up stable nodes, but don't worry if some are still busy */ |
|
remove_all_stable_nodes(); |
|
ksm_scan.seqnr = 0; |
|
return 0; |
|
|
|
error: |
|
mmap_read_unlock(mm); |
|
spin_lock(&ksm_mmlist_lock); |
|
ksm_scan.mm_slot = &ksm_mm_head; |
|
spin_unlock(&ksm_mmlist_lock); |
|
return err; |
|
} |
|
#endif /* CONFIG_SYSFS */ |
|
|
|
static u32 calc_checksum(struct page *page) |
|
{ |
|
u32 checksum; |
|
void *addr = kmap_atomic(page); |
|
checksum = xxhash(addr, PAGE_SIZE, 0); |
|
kunmap_atomic(addr); |
|
return checksum; |
|
} |
|
|
|
static int write_protect_page(struct vm_area_struct *vma, struct page *page, |
|
pte_t *orig_pte) |
|
{ |
|
struct mm_struct *mm = vma->vm_mm; |
|
struct page_vma_mapped_walk pvmw = { |
|
.page = page, |
|
.vma = vma, |
|
}; |
|
int swapped; |
|
int err = -EFAULT; |
|
struct mmu_notifier_range range; |
|
|
|
pvmw.address = page_address_in_vma(page, vma); |
|
if (pvmw.address == -EFAULT) |
|
goto out; |
|
|
|
BUG_ON(PageTransCompound(page)); |
|
|
|
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, |
|
pvmw.address, |
|
pvmw.address + PAGE_SIZE); |
|
mmu_notifier_invalidate_range_start(&range); |
|
|
|
if (!page_vma_mapped_walk(&pvmw)) |
|
goto out_mn; |
|
if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?")) |
|
goto out_unlock; |
|
|
|
if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) || |
|
(pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) || |
|
mm_tlb_flush_pending(mm)) { |
|
pte_t entry; |
|
|
|
swapped = PageSwapCache(page); |
|
flush_cache_page(vma, pvmw.address, page_to_pfn(page)); |
|
/* |
|
* Ok this is tricky, when get_user_pages_fast() run it doesn't |
|
* take any lock, therefore the check that we are going to make |
|
* with the pagecount against the mapcount is racy and |
|
* O_DIRECT can happen right after the check. |
|
* So we clear the pte and flush the tlb before the check |
|
* this assure us that no O_DIRECT can happen after the check |
|
* or in the middle of the check. |
|
* |
|
* No need to notify as we are downgrading page table to read |
|
* only not changing it to point to a new page. |
|
* |
|
* See Documentation/vm/mmu_notifier.rst |
|
*/ |
|
entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte); |
|
/* |
|
* Check that no O_DIRECT or similar I/O is in progress on the |
|
* page |
|
*/ |
|
if (page_mapcount(page) + 1 + swapped != page_count(page)) { |
|
set_pte_at(mm, pvmw.address, pvmw.pte, entry); |
|
goto out_unlock; |
|
} |
|
if (pte_dirty(entry)) |
|
set_page_dirty(page); |
|
|
|
if (pte_protnone(entry)) |
|
entry = pte_mkclean(pte_clear_savedwrite(entry)); |
|
else |
|
entry = pte_mkclean(pte_wrprotect(entry)); |
|
set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry); |
|
} |
|
*orig_pte = *pvmw.pte; |
|
err = 0; |
|
|
|
out_unlock: |
|
page_vma_mapped_walk_done(&pvmw); |
|
out_mn: |
|
mmu_notifier_invalidate_range_end(&range); |
|
out: |
|
return err; |
|
} |
|
|
|
/** |
|
* replace_page - replace page in vma by new ksm page |
|
* @vma: vma that holds the pte pointing to page |
|
* @page: the page we are replacing by kpage |
|
* @kpage: the ksm page we replace page by |
|
* @orig_pte: the original value of the pte |
|
* |
|
* Returns 0 on success, -EFAULT on failure. |
|
*/ |
|
static int replace_page(struct vm_area_struct *vma, struct page *page, |
|
struct page *kpage, pte_t orig_pte) |
|
{ |
|
struct mm_struct *mm = vma->vm_mm; |
|
pmd_t *pmd; |
|
pte_t *ptep; |
|
pte_t newpte; |
|
spinlock_t *ptl; |
|
unsigned long addr; |
|
int err = -EFAULT; |
|
struct mmu_notifier_range range; |
|
|
|
addr = page_address_in_vma(page, vma); |
|
if (addr == -EFAULT) |
|
goto out; |
|
|
|
pmd = mm_find_pmd(mm, addr); |
|
if (!pmd) |
|
goto out; |
|
|
|
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr, |
|
addr + PAGE_SIZE); |
|
mmu_notifier_invalidate_range_start(&range); |
|
|
|
ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); |
|
if (!pte_same(*ptep, orig_pte)) { |
|
pte_unmap_unlock(ptep, ptl); |
|
goto out_mn; |
|
} |
|
|
|
/* |
|
* No need to check ksm_use_zero_pages here: we can only have a |
|
* zero_page here if ksm_use_zero_pages was enabled already. |
|
*/ |
|
if (!is_zero_pfn(page_to_pfn(kpage))) { |
|
get_page(kpage); |
|
page_add_anon_rmap(kpage, vma, addr, false); |
|
newpte = mk_pte(kpage, vma->vm_page_prot); |
|
} else { |
|
newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage), |
|
vma->vm_page_prot)); |
|
/* |
|
* We're replacing an anonymous page with a zero page, which is |
|
* not anonymous. We need to do proper accounting otherwise we |
|
* will get wrong values in /proc, and a BUG message in dmesg |
|
* when tearing down the mm. |
|
*/ |
|
dec_mm_counter(mm, MM_ANONPAGES); |
|
} |
|
|
|
flush_cache_page(vma, addr, pte_pfn(*ptep)); |
|
/* |
|
* No need to notify as we are replacing a read only page with another |
|
* read only page with the same content. |
|
* |
|
* See Documentation/vm/mmu_notifier.rst |
|
*/ |
|
ptep_clear_flush(vma, addr, ptep); |
|
set_pte_at_notify(mm, addr, ptep, newpte); |
|
|
|
page_remove_rmap(page, false); |
|
if (!page_mapped(page)) |
|
try_to_free_swap(page); |
|
put_page(page); |
|
|
|
pte_unmap_unlock(ptep, ptl); |
|
err = 0; |
|
out_mn: |
|
mmu_notifier_invalidate_range_end(&range); |
|
out: |
|
return err; |
|
} |
|
|
|
/* |
|
* try_to_merge_one_page - take two pages and merge them into one |
|
* @vma: the vma that holds the pte pointing to page |
|
* @page: the PageAnon page that we want to replace with kpage |
|
* @kpage: the PageKsm page that we want to map instead of page, |
|
* or NULL the first time when we want to use page as kpage. |
|
* |
|
* This function returns 0 if the pages were merged, -EFAULT otherwise. |
|
*/ |
|
static int try_to_merge_one_page(struct vm_area_struct *vma, |
|
struct page *page, struct page *kpage) |
|
{ |
|
pte_t orig_pte = __pte(0); |
|
int err = -EFAULT; |
|
|
|
if (page == kpage) /* ksm page forked */ |
|
return 0; |
|
|
|
if (!PageAnon(page)) |
|
goto out; |
|
|
|
/* |
|
* We need the page lock to read a stable PageSwapCache in |
|
* write_protect_page(). We use trylock_page() instead of |
|
* lock_page() because we don't want to wait here - we |
|
* prefer to continue scanning and merging different pages, |
|
* then come back to this page when it is unlocked. |
|
*/ |
|
if (!trylock_page(page)) |
|
goto out; |
|
|
|
if (PageTransCompound(page)) { |
|
if (split_huge_page(page)) |
|
goto out_unlock; |
|
} |
|
|
|
/* |
|
* If this anonymous page is mapped only here, its pte may need |
|
* to be write-protected. If it's mapped elsewhere, all of its |
|
* ptes are necessarily already write-protected. But in either |
|
* case, we need to lock and check page_count is not raised. |
|
*/ |
|
if (write_protect_page(vma, page, &orig_pte) == 0) { |
|
if (!kpage) { |
|
/* |
|
* While we hold page lock, upgrade page from |
|
* PageAnon+anon_vma to PageKsm+NULL stable_node: |
|
* stable_tree_insert() will update stable_node. |
|
*/ |
|
set_page_stable_node(page, NULL); |
|
mark_page_accessed(page); |
|
/* |
|
* Page reclaim just frees a clean page with no dirty |
|
* ptes: make sure that the ksm page would be swapped. |
|
*/ |
|
if (!PageDirty(page)) |
|
SetPageDirty(page); |
|
err = 0; |
|
} else if (pages_identical(page, kpage)) |
|
err = replace_page(vma, page, kpage, orig_pte); |
|
} |
|
|
|
if ((vma->vm_flags & VM_LOCKED) && kpage && !err) { |
|
munlock_vma_page(page); |
|
if (!PageMlocked(kpage)) { |
|
unlock_page(page); |
|
lock_page(kpage); |
|
mlock_vma_page(kpage); |
|
page = kpage; /* for final unlock */ |
|
} |
|
} |
|
|
|
out_unlock: |
|
unlock_page(page); |
|
out: |
|
return err; |
|
} |
|
|
|
/* |
|
* try_to_merge_with_ksm_page - like try_to_merge_two_pages, |
|
* but no new kernel page is allocated: kpage must already be a ksm page. |
|
* |
|
* This function returns 0 if the pages were merged, -EFAULT otherwise. |
|
*/ |
|
static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item, |
|
struct page *page, struct page *kpage) |
|
{ |
|
struct mm_struct *mm = rmap_item->mm; |
|
struct vm_area_struct *vma; |
|
int err = -EFAULT; |
|
|
|
mmap_read_lock(mm); |
|
vma = find_mergeable_vma(mm, rmap_item->address); |
|
if (!vma) |
|
goto out; |
|
|
|
err = try_to_merge_one_page(vma, page, kpage); |
|
if (err) |
|
goto out; |
|
|
|
/* Unstable nid is in union with stable anon_vma: remove first */ |
|
remove_rmap_item_from_tree(rmap_item); |
|
|
|
/* Must get reference to anon_vma while still holding mmap_lock */ |
|
rmap_item->anon_vma = vma->anon_vma; |
|
get_anon_vma(vma->anon_vma); |
|
out: |
|
mmap_read_unlock(mm); |
|
return err; |
|
} |
|
|
|
/* |
|
* try_to_merge_two_pages - take two identical pages and prepare them |
|
* to be merged into one page. |
|
* |
|
* This function returns the kpage if we successfully merged two identical |
|
* pages into one ksm page, NULL otherwise. |
|
* |
|
* Note that this function upgrades page to ksm page: if one of the pages |
|
* is already a ksm page, try_to_merge_with_ksm_page should be used. |
|
*/ |
|
static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item, |
|
struct page *page, |
|
struct rmap_item *tree_rmap_item, |
|
struct page *tree_page) |
|
{ |
|
int err; |
|
|
|
err = try_to_merge_with_ksm_page(rmap_item, page, NULL); |
|
if (!err) { |
|
err = try_to_merge_with_ksm_page(tree_rmap_item, |
|
tree_page, page); |
|
/* |
|
* If that fails, we have a ksm page with only one pte |
|
* pointing to it: so break it. |
|
*/ |
|
if (err) |
|
break_cow(rmap_item); |
|
} |
|
return err ? NULL : page; |
|
} |
|
|
|
static __always_inline |
|
bool __is_page_sharing_candidate(struct stable_node *stable_node, int offset) |
|
{ |
|
VM_BUG_ON(stable_node->rmap_hlist_len < 0); |
|
/* |
|
* Check that at least one mapping still exists, otherwise |
|
* there's no much point to merge and share with this |
|
* stable_node, as the underlying tree_page of the other |
|
* sharer is going to be freed soon. |
|
*/ |
|
return stable_node->rmap_hlist_len && |
|
stable_node->rmap_hlist_len + offset < ksm_max_page_sharing; |
|
} |
|
|
|
static __always_inline |
|
bool is_page_sharing_candidate(struct stable_node *stable_node) |
|
{ |
|
return __is_page_sharing_candidate(stable_node, 0); |
|
} |
|
|
|
static struct page *stable_node_dup(struct stable_node **_stable_node_dup, |
|
struct stable_node **_stable_node, |
|
struct rb_root *root, |
|
bool prune_stale_stable_nodes) |
|
{ |
|
struct stable_node *dup, *found = NULL, *stable_node = *_stable_node; |
|
struct hlist_node *hlist_safe; |
|
struct page *_tree_page, *tree_page = NULL; |
|
int nr = 0; |
|
int found_rmap_hlist_len; |
|
|
|
if (!prune_stale_stable_nodes || |
|
time_before(jiffies, stable_node->chain_prune_time + |
|
msecs_to_jiffies( |
|
ksm_stable_node_chains_prune_millisecs))) |
|
prune_stale_stable_nodes = false; |
|
else |
|
stable_node->chain_prune_time = jiffies; |
|
|
|
hlist_for_each_entry_safe(dup, hlist_safe, |
|
&stable_node->hlist, hlist_dup) { |
|
cond_resched(); |
|
/* |
|
* We must walk all stable_node_dup to prune the stale |
|
* stable nodes during lookup. |
|
* |
|
* get_ksm_page can drop the nodes from the |
|
* stable_node->hlist if they point to freed pages |
|
* (that's why we do a _safe walk). The "dup" |
|
* stable_node parameter itself will be freed from |
|
* under us if it returns NULL. |
|
*/ |
|
_tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK); |
|
if (!_tree_page) |
|
continue; |
|
nr += 1; |
|
if (is_page_sharing_candidate(dup)) { |
|
if (!found || |
|
dup->rmap_hlist_len > found_rmap_hlist_len) { |
|
if (found) |
|
put_page(tree_page); |
|
found = dup; |
|
found_rmap_hlist_len = found->rmap_hlist_len; |
|
tree_page = _tree_page; |
|
|
|
/* skip put_page for found dup */ |
|
if (!prune_stale_stable_nodes) |
|
break; |
|
continue; |
|
} |
|
} |
|
put_page(_tree_page); |
|
} |
|
|
|
if (found) { |
|
/* |
|
* nr is counting all dups in the chain only if |
|
* prune_stale_stable_nodes is true, otherwise we may |
|
* break the loop at nr == 1 even if there are |
|
* multiple entries. |
|
*/ |
|
if (prune_stale_stable_nodes && nr == 1) { |
|
/* |
|
* If there's not just one entry it would |
|
* corrupt memory, better BUG_ON. In KSM |
|
* context with no lock held it's not even |
|
* fatal. |
|
*/ |
|
BUG_ON(stable_node->hlist.first->next); |
|
|
|
/* |
|
* There's just one entry and it is below the |
|
* deduplication limit so drop the chain. |
|
*/ |
|
rb_replace_node(&stable_node->node, &found->node, |
|
root); |
|
free_stable_node(stable_node); |
|
ksm_stable_node_chains--; |
|
ksm_stable_node_dups--; |
|
/* |
|
* NOTE: the caller depends on the stable_node |
|
* to be equal to stable_node_dup if the chain |
|
* was collapsed. |
|
*/ |
|
*_stable_node = found; |
|
/* |
|
* Just for robustness, as stable_node is |
|
* otherwise left as a stable pointer, the |
|
* compiler shall optimize it away at build |
|
* time. |
|
*/ |
|
stable_node = NULL; |
|
} else if (stable_node->hlist.first != &found->hlist_dup && |
|
__is_page_sharing_candidate(found, 1)) { |
|
/* |
|
* If the found stable_node dup can accept one |
|
* more future merge (in addition to the one |
|
* that is underway) and is not at the head of |
|
* the chain, put it there so next search will |
|
* be quicker in the !prune_stale_stable_nodes |
|
* case. |
|
* |
|
* NOTE: it would be inaccurate to use nr > 1 |
|
* instead of checking the hlist.first pointer |
|
* directly, because in the |
|
* prune_stale_stable_nodes case "nr" isn't |
|
* the position of the found dup in the chain, |
|
* but the total number of dups in the chain. |
|
*/ |
|
hlist_del(&found->hlist_dup); |
|
hlist_add_head(&found->hlist_dup, |
|
&stable_node->hlist); |
|
} |
|
} |
|
|
|
*_stable_node_dup = found; |
|
return tree_page; |
|
} |
|
|
|
static struct stable_node *stable_node_dup_any(struct stable_node *stable_node, |
|
struct rb_root *root) |
|
{ |
|
if (!is_stable_node_chain(stable_node)) |
|
return stable_node; |
|
if (hlist_empty(&stable_node->hlist)) { |
|
free_stable_node_chain(stable_node, root); |
|
return NULL; |
|
} |
|
return hlist_entry(stable_node->hlist.first, |
|
typeof(*stable_node), hlist_dup); |
|
} |
|
|
|
/* |
|
* Like for get_ksm_page, this function can free the *_stable_node and |
|
* *_stable_node_dup if the returned tree_page is NULL. |
|
* |
|
* It can also free and overwrite *_stable_node with the found |
|
* stable_node_dup if the chain is collapsed (in which case |
|
* *_stable_node will be equal to *_stable_node_dup like if the chain |
|
* never existed). It's up to the caller to verify tree_page is not |
|
* NULL before dereferencing *_stable_node or *_stable_node_dup. |
|
* |
|
* *_stable_node_dup is really a second output parameter of this |
|
* function and will be overwritten in all cases, the caller doesn't |
|
* need to initialize it. |
|
*/ |
|
static struct page *__stable_node_chain(struct stable_node **_stable_node_dup, |
|
struct stable_node **_stable_node, |
|
struct rb_root *root, |
|
bool prune_stale_stable_nodes) |
|
{ |
|
struct stable_node *stable_node = *_stable_node; |
|
if (!is_stable_node_chain(stable_node)) { |
|
if (is_page_sharing_candidate(stable_node)) { |
|
*_stable_node_dup = stable_node; |
|
return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK); |
|
} |
|
/* |
|
* _stable_node_dup set to NULL means the stable_node |
|
* reached the ksm_max_page_sharing limit. |
|
*/ |
|
*_stable_node_dup = NULL; |
|
return NULL; |
|
} |
|
return stable_node_dup(_stable_node_dup, _stable_node, root, |
|
prune_stale_stable_nodes); |
|
} |
|
|
|
static __always_inline struct page *chain_prune(struct stable_node **s_n_d, |
|
struct stable_node **s_n, |
|
struct rb_root *root) |
|
{ |
|
return __stable_node_chain(s_n_d, s_n, root, true); |
|
} |
|
|
|
static __always_inline struct page *chain(struct stable_node **s_n_d, |
|
struct stable_node *s_n, |
|
struct rb_root *root) |
|
{ |
|
struct stable_node *old_stable_node = s_n; |
|
struct page *tree_page; |
|
|
|
tree_page = __stable_node_chain(s_n_d, &s_n, root, false); |
|
/* not pruning dups so s_n cannot have changed */ |
|
VM_BUG_ON(s_n != old_stable_node); |
|
return tree_page; |
|
} |
|
|
|
/* |
|
* stable_tree_search - search for page inside the stable tree |
|
* |
|
* This function checks if there is a page inside the stable tree |
|
* with identical content to the page that we are scanning right now. |
|
* |
|
* This function returns the stable tree node of identical content if found, |
|
* NULL otherwise. |
|
*/ |
|
static struct page *stable_tree_search(struct page *page) |
|
{ |
|
int nid; |
|
struct rb_root *root; |
|
struct rb_node **new; |
|
struct rb_node *parent; |
|
struct stable_node *stable_node, *stable_node_dup, *stable_node_any; |
|
struct stable_node *page_node; |
|
|
|
page_node = page_stable_node(page); |
|
if (page_node && page_node->head != &migrate_nodes) { |
|
/* ksm page forked */ |
|
get_page(page); |
|
return page; |
|
} |
|
|
|
nid = get_kpfn_nid(page_to_pfn(page)); |
|
root = root_stable_tree + nid; |
|
again: |
|
new = &root->rb_node; |
|
parent = NULL; |
|
|
|
while (*new) { |
|
struct page *tree_page; |
|
int ret; |
|
|
|
cond_resched(); |
|
stable_node = rb_entry(*new, struct stable_node, node); |
|
stable_node_any = NULL; |
|
tree_page = chain_prune(&stable_node_dup, &stable_node, root); |
|
/* |
|
* NOTE: stable_node may have been freed by |
|
* chain_prune() if the returned stable_node_dup is |
|
* not NULL. stable_node_dup may have been inserted in |
|
* the rbtree instead as a regular stable_node (in |
|
* order to collapse the stable_node chain if a single |
|
* stable_node dup was found in it). In such case the |
|
* stable_node is overwritten by the calleee to point |
|
* to the stable_node_dup that was collapsed in the |
|
* stable rbtree and stable_node will be equal to |
|
* stable_node_dup like if the chain never existed. |
|
*/ |
|
if (!stable_node_dup) { |
|
/* |
|
* Either all stable_node dups were full in |
|
* this stable_node chain, or this chain was |
|
* empty and should be rb_erased. |
|
*/ |
|
stable_node_any = stable_node_dup_any(stable_node, |
|
root); |
|
if (!stable_node_any) { |
|
/* rb_erase just run */ |
|
goto again; |
|
} |
|
/* |
|
* Take any of the stable_node dups page of |
|
* this stable_node chain to let the tree walk |
|
* continue. All KSM pages belonging to the |
|
* stable_node dups in a stable_node chain |
|
* have the same content and they're |
|
* write protected at all times. Any will work |
|
* fine to continue the walk. |
|
*/ |
|
tree_page = get_ksm_page(stable_node_any, |
|
GET_KSM_PAGE_NOLOCK); |
|
} |
|
VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); |
|
if (!tree_page) { |
|
/* |
|
* If we walked over a stale stable_node, |
|
* get_ksm_page() will call rb_erase() and it |
|
* may rebalance the tree from under us. So |
|
* restart the search from scratch. Returning |
|
* NULL would be safe too, but we'd generate |
|
* false negative insertions just because some |
|
* stable_node was stale. |
|
*/ |
|
goto again; |
|
} |
|
|
|
ret = memcmp_pages(page, tree_page); |
|
put_page(tree_page); |
|
|
|
parent = *new; |
|
if (ret < 0) |
|
new = &parent->rb_left; |
|
else if (ret > 0) |
|
new = &parent->rb_right; |
|
else { |
|
if (page_node) { |
|
VM_BUG_ON(page_node->head != &migrate_nodes); |
|
/* |
|
* Test if the migrated page should be merged |
|
* into a stable node dup. If the mapcount is |
|
* 1 we can migrate it with another KSM page |
|
* without adding it to the chain. |
|
*/ |
|
if (page_mapcount(page) > 1) |
|
goto chain_append; |
|
} |
|
|
|
if (!stable_node_dup) { |
|
/* |
|
* If the stable_node is a chain and |
|
* we got a payload match in memcmp |
|
* but we cannot merge the scanned |
|
* page in any of the existing |
|
* stable_node dups because they're |
|
* all full, we need to wait the |
|
* scanned page to find itself a match |
|
* in the unstable tree to create a |
|
* brand new KSM page to add later to |
|
* the dups of this stable_node. |
|
*/ |
|
return NULL; |
|
} |
|
|
|
/* |
|
* Lock and unlock the stable_node's page (which |
|
* might already have been migrated) so that page |
|
* migration is sure to notice its raised count. |
|
* It would be more elegant to return stable_node |
|
* than kpage, but that involves more changes. |
|
*/ |
|
tree_page = get_ksm_page(stable_node_dup, |
|
GET_KSM_PAGE_TRYLOCK); |
|
|
|
if (PTR_ERR(tree_page) == -EBUSY) |
|
return ERR_PTR(-EBUSY); |
|
|
|
if (unlikely(!tree_page)) |
|
/* |
|
* The tree may have been rebalanced, |
|
* so re-evaluate parent and new. |
|
*/ |
|
goto again; |
|
unlock_page(tree_page); |
|
|
|
if (get_kpfn_nid(stable_node_dup->kpfn) != |
|
NUMA(stable_node_dup->nid)) { |
|
put_page(tree_page); |
|
goto replace; |
|
} |
|
return tree_page; |
|
} |
|
} |
|
|
|
if (!page_node) |
|
return NULL; |
|
|
|
list_del(&page_node->list); |
|
DO_NUMA(page_node->nid = nid); |
|
rb_link_node(&page_node->node, parent, new); |
|
rb_insert_color(&page_node->node, root); |
|
out: |
|
if (is_page_sharing_candidate(page_node)) { |
|
get_page(page); |
|
return page; |
|
} else |
|
return NULL; |
|
|
|
replace: |
|
/* |
|
* If stable_node was a chain and chain_prune collapsed it, |
|
* stable_node has been updated to be the new regular |
|
* stable_node. A collapse of the chain is indistinguishable |
|
* from the case there was no chain in the stable |
|
* rbtree. Otherwise stable_node is the chain and |
|
* stable_node_dup is the dup to replace. |
|
*/ |
|
if (stable_node_dup == stable_node) { |
|
VM_BUG_ON(is_stable_node_chain(stable_node_dup)); |
|
VM_BUG_ON(is_stable_node_dup(stable_node_dup)); |
|
/* there is no chain */ |
|
if (page_node) { |
|
VM_BUG_ON(page_node->head != &migrate_nodes); |
|
list_del(&page_node->list); |
|
DO_NUMA(page_node->nid = nid); |
|
rb_replace_node(&stable_node_dup->node, |
|
&page_node->node, |
|
root); |
|
if (is_page_sharing_candidate(page_node)) |
|
get_page(page); |
|
else |
|
page = NULL; |
|
} else { |
|
rb_erase(&stable_node_dup->node, root); |
|
page = NULL; |
|
} |
|
} else { |
|
VM_BUG_ON(!is_stable_node_chain(stable_node)); |
|
__stable_node_dup_del(stable_node_dup); |
|
if (page_node) { |
|
VM_BUG_ON(page_node->head != &migrate_nodes); |
|
list_del(&page_node->list); |
|
DO_NUMA(page_node->nid = nid); |
|
stable_node_chain_add_dup(page_node, stable_node); |
|
if (is_page_sharing_candidate(page_node)) |
|
get_page(page); |
|
else |
|
page = NULL; |
|
} else { |
|
page = NULL; |
|
} |
|
} |
|
stable_node_dup->head = &migrate_nodes; |
|
list_add(&stable_node_dup->list, stable_node_dup->head); |
|
return page; |
|
|
|
chain_append: |
|
/* stable_node_dup could be null if it reached the limit */ |
|
if (!stable_node_dup) |
|
stable_node_dup = stable_node_any; |
|
/* |
|
* If stable_node was a chain and chain_prune collapsed it, |
|
* stable_node has been updated to be the new regular |
|
* stable_node. A collapse of the chain is indistinguishable |
|
* from the case there was no chain in the stable |
|
* rbtree. Otherwise stable_node is the chain and |
|
* stable_node_dup is the dup to replace. |
|
*/ |
|
if (stable_node_dup == stable_node) { |
|
VM_BUG_ON(is_stable_node_dup(stable_node_dup)); |
|
/* chain is missing so create it */ |
|
stable_node = alloc_stable_node_chain(stable_node_dup, |
|
root); |
|
if (!stable_node) |
|
return NULL; |
|
} |
|
/* |
|
* Add this stable_node dup that was |
|
* migrated to the stable_node chain |
|
* of the current nid for this page |
|
* content. |
|
*/ |
|
VM_BUG_ON(!is_stable_node_dup(stable_node_dup)); |
|
VM_BUG_ON(page_node->head != &migrate_nodes); |
|
list_del(&page_node->list); |
|
DO_NUMA(page_node->nid = nid); |
|
stable_node_chain_add_dup(page_node, stable_node); |
|
goto out; |
|
} |
|
|
|
/* |
|
* stable_tree_insert - insert stable tree node pointing to new ksm page |
|
* into the stable tree. |
|
* |
|
* This function returns the stable tree node just allocated on success, |
|
* NULL otherwise. |
|
*/ |
|
static struct stable_node *stable_tree_insert(struct page *kpage) |
|
{ |
|
int nid; |
|
unsigned long kpfn; |
|
struct rb_root *root; |
|
struct rb_node **new; |
|
struct rb_node *parent; |
|
struct stable_node *stable_node, *stable_node_dup, *stable_node_any; |
|
bool need_chain = false; |
|
|
|
kpfn = page_to_pfn(kpage); |
|
nid = get_kpfn_nid(kpfn); |
|
root = root_stable_tree + nid; |
|
again: |
|
parent = NULL; |
|
new = &root->rb_node; |
|
|
|
while (*new) { |
|
struct page *tree_page; |
|
int ret; |
|
|
|
cond_resched(); |
|
stable_node = rb_entry(*new, struct stable_node, node); |
|
stable_node_any = NULL; |
|
tree_page = chain(&stable_node_dup, stable_node, root); |
|
if (!stable_node_dup) { |
|
/* |
|
* Either all stable_node dups were full in |
|
* this stable_node chain, or this chain was |
|
* empty and should be rb_erased. |
|
*/ |
|
stable_node_any = stable_node_dup_any(stable_node, |
|
root); |
|
if (!stable_node_any) { |
|
/* rb_erase just run */ |
|
goto again; |
|
} |
|
/* |
|
* Take any of the stable_node dups page of |
|
* this stable_node chain to let the tree walk |
|
* continue. All KSM pages belonging to the |
|
* stable_node dups in a stable_node chain |
|
* have the same content and they're |
|
* write protected at all times. Any will work |
|
* fine to continue the walk. |
|
*/ |
|
tree_page = get_ksm_page(stable_node_any, |
|
GET_KSM_PAGE_NOLOCK); |
|
} |
|
VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); |
|
if (!tree_page) { |
|
/* |
|
* If we walked over a stale stable_node, |
|
* get_ksm_page() will call rb_erase() and it |
|
* may rebalance the tree from under us. So |
|
* restart the search from scratch. Returning |
|
* NULL would be safe too, but we'd generate |
|
* false negative insertions just because some |
|
* stable_node was stale. |
|
*/ |
|
goto again; |
|
} |
|
|
|
ret = memcmp_pages(kpage, tree_page); |
|
put_page(tree_page); |
|
|
|
parent = *new; |
|
if (ret < 0) |
|
new = &parent->rb_left; |
|
else if (ret > 0) |
|
new = &parent->rb_right; |
|
else { |
|
need_chain = true; |
|
break; |
|
} |
|
} |
|
|
|
stable_node_dup = alloc_stable_node(); |
|
if (!stable_node_dup) |
|
return NULL; |
|
|
|
INIT_HLIST_HEAD(&stable_node_dup->hlist); |
|
stable_node_dup->kpfn = kpfn; |
|
set_page_stable_node(kpage, stable_node_dup); |
|
stable_node_dup->rmap_hlist_len = 0; |
|
DO_NUMA(stable_node_dup->nid = nid); |
|
if (!need_chain) { |
|
rb_link_node(&stable_node_dup->node, parent, new); |
|
rb_insert_color(&stable_node_dup->node, root); |
|
} else { |
|
if (!is_stable_node_chain(stable_node)) { |
|
struct stable_node *orig = stable_node; |
|
/* chain is missing so create it */ |
|
stable_node = alloc_stable_node_chain(orig, root); |
|
if (!stable_node) { |
|
free_stable_node(stable_node_dup); |
|
return NULL; |
|
} |
|
} |
|
stable_node_chain_add_dup(stable_node_dup, stable_node); |
|
} |
|
|
|
return stable_node_dup; |
|
} |
|
|
|
/* |
|
* unstable_tree_search_insert - search for identical page, |
|
* else insert rmap_item into the unstable tree. |
|
* |
|
* This function searches for a page in the unstable tree identical to the |
|
* page currently being scanned; and if no identical page is found in the |
|
* tree, we insert rmap_item as a new object into the unstable tree. |
|
* |
|
* This function returns pointer to rmap_item found to be identical |
|
* to the currently scanned page, NULL otherwise. |
|
* |
|
* This function does both searching and inserting, because they share |
|
* the same walking algorithm in an rbtree. |
|
*/ |
|
static |
|
struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item, |
|
struct page *page, |
|
struct page **tree_pagep) |
|
{ |
|
struct rb_node **new; |
|
struct rb_root *root; |
|
struct rb_node *parent = NULL; |
|
int nid; |
|
|
|
nid = get_kpfn_nid(page_to_pfn(page)); |
|
root = root_unstable_tree + nid; |
|
new = &root->rb_node; |
|
|
|
while (*new) { |
|
struct rmap_item *tree_rmap_item; |
|
struct page *tree_page; |
|
int ret; |
|
|
|
cond_resched(); |
|
tree_rmap_item = rb_entry(*new, struct rmap_item, node); |
|
tree_page = get_mergeable_page(tree_rmap_item); |
|
if (!tree_page) |
|
return NULL; |
|
|
|
/* |
|
* Don't substitute a ksm page for a forked page. |
|
*/ |
|
if (page == tree_page) { |
|
put_page(tree_page); |
|
return NULL; |
|
} |
|
|
|
ret = memcmp_pages(page, tree_page); |
|
|
|
parent = *new; |
|
if (ret < 0) { |
|
put_page(tree_page); |
|
new = &parent->rb_left; |
|
} else if (ret > 0) { |
|
put_page(tree_page); |
|
new = &parent->rb_right; |
|
} else if (!ksm_merge_across_nodes && |
|
page_to_nid(tree_page) != nid) { |
|
/* |
|
* If tree_page has been migrated to another NUMA node, |
|
* it will be flushed out and put in the right unstable |
|
* tree next time: only merge with it when across_nodes. |
|
*/ |
|
put_page(tree_page); |
|
return NULL; |
|
} else { |
|
*tree_pagep = tree_page; |
|
return tree_rmap_item; |
|
} |
|
} |
|
|
|
rmap_item->address |= UNSTABLE_FLAG; |
|
rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK); |
|
DO_NUMA(rmap_item->nid = nid); |
|
rb_link_node(&rmap_item->node, parent, new); |
|
rb_insert_color(&rmap_item->node, root); |
|
|
|
ksm_pages_unshared++; |
|
return NULL; |
|
} |
|
|
|
/* |
|
* stable_tree_append - add another rmap_item to the linked list of |
|
* rmap_items hanging off a given node of the stable tree, all sharing |
|
* the same ksm page. |
|
*/ |
|
static void stable_tree_append(struct rmap_item *rmap_item, |
|
struct stable_node *stable_node, |
|
bool max_page_sharing_bypass) |
|
{ |
|
/* |
|
* rmap won't find this mapping if we don't insert the |
|
* rmap_item in the right stable_node |
|
* duplicate. page_migration could break later if rmap breaks, |
|
* so we can as well crash here. We really need to check for |
|
* rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check |
|
* for other negative values as an underflow if detected here |
|
* for the first time (and not when decreasing rmap_hlist_len) |
|
* would be sign of memory corruption in the stable_node. |
|
*/ |
|
BUG_ON(stable_node->rmap_hlist_len < 0); |
|
|
|
stable_node->rmap_hlist_len++; |
|
if (!max_page_sharing_bypass) |
|
/* possibly non fatal but unexpected overflow, only warn */ |
|
WARN_ON_ONCE(stable_node->rmap_hlist_len > |
|
ksm_max_page_sharing); |
|
|
|
rmap_item->head = stable_node; |
|
rmap_item->address |= STABLE_FLAG; |
|
hlist_add_head(&rmap_item->hlist, &stable_node->hlist); |
|
|
|
if (rmap_item->hlist.next) |
|
ksm_pages_sharing++; |
|
else |
|
ksm_pages_shared++; |
|
} |
|
|
|
/* |
|
* cmp_and_merge_page - first see if page can be merged into the stable tree; |
|
* if not, compare checksum to previous and if it's the same, see if page can |
|
* be inserted into the unstable tree, or merged with a page already there and |
|
* both transferred to the stable tree. |
|
* |
|
* @page: the page that we are searching identical page to. |
|
* @rmap_item: the reverse mapping into the virtual address of this page |
|
*/ |
|
static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) |
|
{ |
|
struct mm_struct *mm = rmap_item->mm; |
|
struct rmap_item *tree_rmap_item; |
|
struct page *tree_page = NULL; |
|
struct stable_node *stable_node; |
|
struct page *kpage; |
|
unsigned int checksum; |
|
int err; |
|
bool max_page_sharing_bypass = false; |
|
|
|
stable_node = page_stable_node(page); |
|
if (stable_node) { |
|
if (stable_node->head != &migrate_nodes && |
|
get_kpfn_nid(READ_ONCE(stable_node->kpfn)) != |
|
NUMA(stable_node->nid)) { |
|
stable_node_dup_del(stable_node); |
|
stable_node->head = &migrate_nodes; |
|
list_add(&stable_node->list, stable_node->head); |
|
} |
|
if (stable_node->head != &migrate_nodes && |
|
rmap_item->head == stable_node) |
|
return; |
|
/* |
|
* If it's a KSM fork, allow it to go over the sharing limit |
|
* without warnings. |
|
*/ |
|
if (!is_page_sharing_candidate(stable_node)) |
|
max_page_sharing_bypass = true; |
|
} |
|
|
|
/* We first start with searching the page inside the stable tree */ |
|
kpage = stable_tree_search(page); |
|
if (kpage == page && rmap_item->head == stable_node) { |
|
put_page(kpage); |
|
return; |
|
} |
|
|
|
remove_rmap_item_from_tree(rmap_item); |
|
|
|
if (kpage) { |
|
if (PTR_ERR(kpage) == -EBUSY) |
|
return; |
|
|
|
err = try_to_merge_with_ksm_page(rmap_item, page, kpage); |
|
if (!err) { |
|
/* |
|
* The page was successfully merged: |
|
* add its rmap_item to the stable tree. |
|
*/ |
|
lock_page(kpage); |
|
stable_tree_append(rmap_item, page_stable_node(kpage), |
|
max_page_sharing_bypass); |
|
unlock_page(kpage); |
|
} |
|
put_page(kpage); |
|
return; |
|
} |
|
|
|
/* |
|
* If the hash value of the page has changed from the last time |
|
* we calculated it, this page is changing frequently: therefore we |
|
* don't want to insert it in the unstable tree, and we don't want |
|
* to waste our time searching for something identical to it there. |
|
*/ |
|
checksum = calc_checksum(page); |
|
if (rmap_item->oldchecksum != checksum) { |
|
rmap_item->oldchecksum = checksum; |
|
return; |
|
} |
|
|
|
/* |
|
* Same checksum as an empty page. We attempt to merge it with the |
|
* appropriate zero page if the user enabled this via sysfs. |
|
*/ |
|
if (ksm_use_zero_pages && (checksum == zero_checksum)) { |
|
struct vm_area_struct *vma; |
|
|
|
mmap_read_lock(mm); |
|
vma = find_mergeable_vma(mm, rmap_item->address); |
|
if (vma) { |
|
err = try_to_merge_one_page(vma, page, |
|
ZERO_PAGE(rmap_item->address)); |
|
} else { |
|
/* |
|
* If the vma is out of date, we do not need to |
|
* continue. |
|
*/ |
|
err = 0; |
|
} |
|
mmap_read_unlock(mm); |
|
/* |
|
* In case of failure, the page was not really empty, so we |
|
* need to continue. Otherwise we're done. |
|
*/ |
|
if (!err) |
|
return; |
|
} |
|
tree_rmap_item = |
|
unstable_tree_search_insert(rmap_item, page, &tree_page); |
|
if (tree_rmap_item) { |
|
bool split; |
|
|
|
kpage = try_to_merge_two_pages(rmap_item, page, |
|
tree_rmap_item, tree_page); |
|
/* |
|
* If both pages we tried to merge belong to the same compound |
|
* page, then we actually ended up increasing the reference |
|
* count of the same compound page twice, and split_huge_page |
|
* failed. |
|
* Here we set a flag if that happened, and we use it later to |
|
* try split_huge_page again. Since we call put_page right |
|
* afterwards, the reference count will be correct and |
|
* split_huge_page should succeed. |
|
*/ |
|
split = PageTransCompound(page) |
|
&& compound_head(page) == compound_head(tree_page); |
|
put_page(tree_page); |
|
if (kpage) { |
|
/* |
|
* The pages were successfully merged: insert new |
|
* node in the stable tree and add both rmap_items. |
|
*/ |
|
lock_page(kpage); |
|
stable_node = stable_tree_insert(kpage); |
|
if (stable_node) { |
|
stable_tree_append(tree_rmap_item, stable_node, |
|
false); |
|
stable_tree_append(rmap_item, stable_node, |
|
false); |
|
} |
|
unlock_page(kpage); |
|
|
|
/* |
|
* If we fail to insert the page into the stable tree, |
|
* we will have 2 virtual addresses that are pointing |
|
* to a ksm page left outside the stable tree, |
|
* in which case we need to break_cow on both. |
|
*/ |
|
if (!stable_node) { |
|
break_cow(tree_rmap_item); |
|
break_cow(rmap_item); |
|
} |
|
} else if (split) { |
|
/* |
|
* We are here if we tried to merge two pages and |
|
* failed because they both belonged to the same |
|
* compound page. We will split the page now, but no |
|
* merging will take place. |
|
* We do not want to add the cost of a full lock; if |
|
* the page is locked, it is better to skip it and |
|
* perhaps try again later. |
|
*/ |
|
if (!trylock_page(page)) |
|
return; |
|
split_huge_page(page); |
|
unlock_page(page); |
|
} |
|
} |
|
} |
|
|
|
static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, |
|
struct rmap_item **rmap_list, |
|
unsigned long addr) |
|
{ |
|
struct rmap_item *rmap_item; |
|
|
|
while (*rmap_list) { |
|
rmap_item = *rmap_list; |
|
if ((rmap_item->address & PAGE_MASK) == addr) |
|
return rmap_item; |
|
if (rmap_item->address > addr) |
|
break; |
|
*rmap_list = rmap_item->rmap_list; |
|
remove_rmap_item_from_tree(rmap_item); |
|
free_rmap_item(rmap_item); |
|
} |
|
|
|
rmap_item = alloc_rmap_item(); |
|
if (rmap_item) { |
|
/* It has already been zeroed */ |
|
rmap_item->mm = mm_slot->mm; |
|
rmap_item->address = addr; |
|
rmap_item->rmap_list = *rmap_list; |
|
*rmap_list = rmap_item; |
|
} |
|
return rmap_item; |
|
} |
|
|
|
static struct rmap_item *scan_get_next_rmap_item(struct page **page) |
|
{ |
|
struct mm_struct *mm; |
|
struct mm_slot *slot; |
|
struct vm_area_struct *vma; |
|
struct rmap_item *rmap_item; |
|
int nid; |
|
|
|
if (list_empty(&ksm_mm_head.mm_list)) |
|
return NULL; |
|
|
|
slot = ksm_scan.mm_slot; |
|
if (slot == &ksm_mm_head) { |
|
/* |
|
* A number of pages can hang around indefinitely on per-cpu |
|
* pagevecs, raised page count preventing write_protect_page |
|
* from merging them. Though it doesn't really matter much, |
|
* it is puzzling to see some stuck in pages_volatile until |
|
* other activity jostles them out, and they also prevented |
|
* LTP's KSM test from succeeding deterministically; so drain |
|
* them here (here rather than on entry to ksm_do_scan(), |
|
* so we don't IPI too often when pages_to_scan is set low). |
|
*/ |
|
lru_add_drain_all(); |
|
|
|
/* |
|
* Whereas stale stable_nodes on the stable_tree itself |
|
* get pruned in the regular course of stable_tree_search(), |
|
* those moved out to the migrate_nodes list can accumulate: |
|
* so prune them once before each full scan. |
|
*/ |
|
if (!ksm_merge_across_nodes) { |
|
struct stable_node *stable_node, *next; |
|
struct page *page; |
|
|
|
list_for_each_entry_safe(stable_node, next, |
|
&migrate_nodes, list) { |
|
page = get_ksm_page(stable_node, |
|
GET_KSM_PAGE_NOLOCK); |
|
if (page) |
|
put_page(page); |
|
cond_resched(); |
|
} |
|
} |
|
|
|
for (nid = 0; nid < ksm_nr_node_ids; nid++) |
|
root_unstable_tree[nid] = RB_ROOT; |
|
|
|
spin_lock(&ksm_mmlist_lock); |
|
slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); |
|
ksm_scan.mm_slot = slot; |
|
spin_unlock(&ksm_mmlist_lock); |
|
/* |
|
* Although we tested list_empty() above, a racing __ksm_exit |
|
* of the last mm on the list may have removed it since then. |
|
*/ |
|
if (slot == &ksm_mm_head) |
|
return NULL; |
|
next_mm: |
|
ksm_scan.address = 0; |
|
ksm_scan.rmap_list = &slot->rmap_list; |
|
} |
|
|
|
mm = slot->mm; |
|
mmap_read_lock(mm); |
|
if (ksm_test_exit(mm)) |
|
vma = NULL; |
|
else |
|
vma = find_vma(mm, ksm_scan.address); |
|
|
|
for (; vma; vma = vma->vm_next) { |
|
if (!(vma->vm_flags & VM_MERGEABLE)) |
|
continue; |
|
if (ksm_scan.address < vma->vm_start) |
|
ksm_scan.address = vma->vm_start; |
|
if (!vma->anon_vma) |
|
ksm_scan.address = vma->vm_end; |
|
|
|
while (ksm_scan.address < vma->vm_end) { |
|
if (ksm_test_exit(mm)) |
|
break; |
|
*page = follow_page(vma, ksm_scan.address, FOLL_GET); |
|
if (IS_ERR_OR_NULL(*page)) { |
|
ksm_scan.address += PAGE_SIZE; |
|
cond_resched(); |
|
continue; |
|
} |
|
if (PageAnon(*page)) { |
|
flush_anon_page(vma, *page, ksm_scan.address); |
|
flush_dcache_page(*page); |
|
rmap_item = get_next_rmap_item(slot, |
|
ksm_scan.rmap_list, ksm_scan.address); |
|
if (rmap_item) { |
|
ksm_scan.rmap_list = |
|
&rmap_item->rmap_list; |
|
ksm_scan.address += PAGE_SIZE; |
|
} else |
|
put_page(*page); |
|
mmap_read_unlock(mm); |
|
return rmap_item; |
|
} |
|
put_page(*page); |
|
ksm_scan.address += PAGE_SIZE; |
|
cond_resched(); |
|
} |
|
} |
|
|
|
if (ksm_test_exit(mm)) { |
|
ksm_scan.address = 0; |
|
ksm_scan.rmap_list = &slot->rmap_list; |
|
} |
|
/* |
|
* Nuke all the rmap_items that are above this current rmap: |
|
* because there were no VM_MERGEABLE vmas with such addresses. |
|
*/ |
|
remove_trailing_rmap_items(ksm_scan.rmap_list); |
|
|
|
spin_lock(&ksm_mmlist_lock); |
|
ksm_scan.mm_slot = list_entry(slot->mm_list.next, |
|
struct mm_slot, mm_list); |
|
if (ksm_scan.address == 0) { |
|
/* |
|
* We've completed a full scan of all vmas, holding mmap_lock |
|
* throughout, and found no VM_MERGEABLE: so do the same as |
|
* __ksm_exit does to remove this mm from all our lists now. |
|
* This applies either when cleaning up after __ksm_exit |
|
* (but beware: we can reach here even before __ksm_exit), |
|
* or when all VM_MERGEABLE areas have been unmapped (and |
|
* mmap_lock then protects against race with MADV_MERGEABLE). |
|
*/ |
|
hash_del(&slot->link); |
|
list_del(&slot->mm_list); |
|
spin_unlock(&ksm_mmlist_lock); |
|
|
|
free_mm_slot(slot); |
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags); |
|
mmap_read_unlock(mm); |
|
mmdrop(mm); |
|
} else { |
|
mmap_read_unlock(mm); |
|
/* |
|
* mmap_read_unlock(mm) first because after |
|
* spin_unlock(&ksm_mmlist_lock) run, the "mm" may |
|
* already have been freed under us by __ksm_exit() |
|
* because the "mm_slot" is still hashed and |
|
* ksm_scan.mm_slot doesn't point to it anymore. |
|
*/ |
|
spin_unlock(&ksm_mmlist_lock); |
|
} |
|
|
|
/* Repeat until we've completed scanning the whole list */ |
|
slot = ksm_scan.mm_slot; |
|
if (slot != &ksm_mm_head) |
|
goto next_mm; |
|
|
|
ksm_scan.seqnr++; |
|
return NULL; |
|
} |
|
|
|
/** |
|
* ksm_do_scan - the ksm scanner main worker function. |
|
* @scan_npages: number of pages we want to scan before we return. |
|
*/ |
|
static void ksm_do_scan(unsigned int scan_npages) |
|
{ |
|
struct rmap_item *rmap_item; |
|
struct page *page; |
|
|
|
while (scan_npages-- && likely(!freezing(current))) { |
|
cond_resched(); |
|
rmap_item = scan_get_next_rmap_item(&page); |
|
if (!rmap_item) |
|
return; |
|
cmp_and_merge_page(page, rmap_item); |
|
put_page(page); |
|
} |
|
} |
|
|
|
static int ksmd_should_run(void) |
|
{ |
|
return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list); |
|
} |
|
|
|
static int ksm_scan_thread(void *nothing) |
|
{ |
|
unsigned int sleep_ms; |
|
|
|
set_freezable(); |
|
set_user_nice(current, 5); |
|
|
|
while (!kthread_should_stop()) { |
|
mutex_lock(&ksm_thread_mutex); |
|
wait_while_offlining(); |
|
if (ksmd_should_run()) |
|
ksm_do_scan(ksm_thread_pages_to_scan); |
|
mutex_unlock(&ksm_thread_mutex); |
|
|
|
try_to_freeze(); |
|
|
|
if (ksmd_should_run()) { |
|
sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs); |
|
wait_event_interruptible_timeout(ksm_iter_wait, |
|
sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs), |
|
msecs_to_jiffies(sleep_ms)); |
|
} else { |
|
wait_event_freezable(ksm_thread_wait, |
|
ksmd_should_run() || kthread_should_stop()); |
|
} |
|
} |
|
return 0; |
|
} |
|
|
|
int ksm_madvise(struct vm_area_struct *vma, unsigned long start, |
|
unsigned long end, int advice, unsigned long *vm_flags) |
|
{ |
|
struct mm_struct *mm = vma->vm_mm; |
|
int err; |
|
|
|
switch (advice) { |
|
case MADV_MERGEABLE: |
|
/* |
|
* Be somewhat over-protective for now! |
|
*/ |
|
if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE | |
|
VM_PFNMAP | VM_IO | VM_DONTEXPAND | |
|
VM_HUGETLB | VM_MIXEDMAP)) |
|
return 0; /* just ignore the advice */ |
|
|
|
if (vma_is_dax(vma)) |
|
return 0; |
|
|
|
#ifdef VM_SAO |
|
if (*vm_flags & VM_SAO) |
|
return 0; |
|
#endif |
|
#ifdef VM_SPARC_ADI |
|
if (*vm_flags & VM_SPARC_ADI) |
|
return 0; |
|
#endif |
|
|
|
if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) { |
|
err = __ksm_enter(mm); |
|
if (err) |
|
return err; |
|
} |
|
|
|
*vm_flags |= VM_MERGEABLE; |
|
break; |
|
|
|
case MADV_UNMERGEABLE: |
|
if (!(*vm_flags & VM_MERGEABLE)) |
|
return 0; /* just ignore the advice */ |
|
|
|
if (vma->anon_vma) { |
|
err = unmerge_ksm_pages(vma, start, end); |
|
if (err) |
|
return err; |
|
} |
|
|
|
*vm_flags &= ~VM_MERGEABLE; |
|
break; |
|
} |
|
|
|
return 0; |
|
} |
|
EXPORT_SYMBOL_GPL(ksm_madvise); |
|
|
|
int __ksm_enter(struct mm_struct *mm) |
|
{ |
|
struct mm_slot *mm_slot; |
|
int needs_wakeup; |
|
|
|
mm_slot = alloc_mm_slot(); |
|
if (!mm_slot) |
|
return -ENOMEM; |
|
|
|
/* Check ksm_run too? Would need tighter locking */ |
|
needs_wakeup = list_empty(&ksm_mm_head.mm_list); |
|
|
|
spin_lock(&ksm_mmlist_lock); |
|
insert_to_mm_slots_hash(mm, mm_slot); |
|
/* |
|
* When KSM_RUN_MERGE (or KSM_RUN_STOP), |
|
* insert just behind the scanning cursor, to let the area settle |
|
* down a little; when fork is followed by immediate exec, we don't |
|
* want ksmd to waste time setting up and tearing down an rmap_list. |
|
* |
|
* But when KSM_RUN_UNMERGE, it's important to insert ahead of its |
|
* scanning cursor, otherwise KSM pages in newly forked mms will be |
|
* missed: then we might as well insert at the end of the list. |
|
*/ |
|
if (ksm_run & KSM_RUN_UNMERGE) |
|
list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list); |
|
else |
|
list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list); |
|
spin_unlock(&ksm_mmlist_lock); |
|
|
|
set_bit(MMF_VM_MERGEABLE, &mm->flags); |
|
mmgrab(mm); |
|
|
|
if (needs_wakeup) |
|
wake_up_interruptible(&ksm_thread_wait); |
|
|
|
return 0; |
|
} |
|
|
|
void __ksm_exit(struct mm_struct *mm) |
|
{ |
|
struct mm_slot *mm_slot; |
|
int easy_to_free = 0; |
|
|
|
/* |
|
* This process is exiting: if it's straightforward (as is the |
|
* case when ksmd was never running), free mm_slot immediately. |
|
* But if it's at the cursor or has rmap_items linked to it, use |
|
* mmap_lock to synchronize with any break_cows before pagetables |
|
* are freed, and leave the mm_slot on the list for ksmd to free. |
|
* Beware: ksm may already have noticed it exiting and freed the slot. |
|
*/ |
|
|
|
spin_lock(&ksm_mmlist_lock); |
|
mm_slot = get_mm_slot(mm); |
|
if (mm_slot && ksm_scan.mm_slot != mm_slot) { |
|
if (!mm_slot->rmap_list) { |
|
hash_del(&mm_slot->link); |
|
list_del(&mm_slot->mm_list); |
|
easy_to_free = 1; |
|
} else { |
|
list_move(&mm_slot->mm_list, |
|
&ksm_scan.mm_slot->mm_list); |
|
} |
|
} |
|
spin_unlock(&ksm_mmlist_lock); |
|
|
|
if (easy_to_free) { |
|
free_mm_slot(mm_slot); |
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags); |
|
mmdrop(mm); |
|
} else if (mm_slot) { |
|
mmap_write_lock(mm); |
|
mmap_write_unlock(mm); |
|
} |
|
} |
|
|
|
struct page *ksm_might_need_to_copy(struct page *page, |
|
struct vm_area_struct *vma, unsigned long address) |
|
{ |
|
struct anon_vma *anon_vma = page_anon_vma(page); |
|
struct page *new_page; |
|
|
|
if (PageKsm(page)) { |
|
if (page_stable_node(page) && |
|
!(ksm_run & KSM_RUN_UNMERGE)) |
|
return page; /* no need to copy it */ |
|
} else if (!anon_vma) { |
|
return page; /* no need to copy it */ |
|
} else if (anon_vma->root == vma->anon_vma->root && |
|
page->index == linear_page_index(vma, address)) { |
|
return page; /* still no need to copy it */ |
|
} |
|
if (!PageUptodate(page)) |
|
return page; /* let do_swap_page report the error */ |
|
|
|
new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); |
|
if (new_page && mem_cgroup_charge(new_page, vma->vm_mm, GFP_KERNEL)) { |
|
put_page(new_page); |
|
new_page = NULL; |
|
} |
|
if (new_page) { |
|
copy_user_highpage(new_page, page, address, vma); |
|
|
|
SetPageDirty(new_page); |
|
__SetPageUptodate(new_page); |
|
__SetPageLocked(new_page); |
|
} |
|
|
|
return new_page; |
|
} |
|
|
|
void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc) |
|
{ |
|
struct stable_node *stable_node; |
|
struct rmap_item *rmap_item; |
|
int search_new_forks = 0; |
|
|
|
VM_BUG_ON_PAGE(!PageKsm(page), page); |
|
|
|
/* |
|
* Rely on the page lock to protect against concurrent modifications |
|
* to that page's node of the stable tree. |
|
*/ |
|
VM_BUG_ON_PAGE(!PageLocked(page), page); |
|
|
|
stable_node = page_stable_node(page); |
|
if (!stable_node) |
|
return; |
|
again: |
|
hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { |
|
struct anon_vma *anon_vma = rmap_item->anon_vma; |
|
struct anon_vma_chain *vmac; |
|
struct vm_area_struct *vma; |
|
|
|
cond_resched(); |
|
anon_vma_lock_read(anon_vma); |
|
anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root, |
|
0, ULONG_MAX) { |
|
unsigned long addr; |
|
|
|
cond_resched(); |
|
vma = vmac->vma; |
|
|
|
/* Ignore the stable/unstable/sqnr flags */ |
|
addr = rmap_item->address & PAGE_MASK; |
|
|
|
if (addr < vma->vm_start || addr >= vma->vm_end) |
|
continue; |
|
/* |
|
* Initially we examine only the vma which covers this |
|
* rmap_item; but later, if there is still work to do, |
|
* we examine covering vmas in other mms: in case they |
|
* were forked from the original since ksmd passed. |
|
*/ |
|
if ((rmap_item->mm == vma->vm_mm) == search_new_forks) |
|
continue; |
|
|
|
if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg)) |
|
continue; |
|
|
|
if (!rwc->rmap_one(page, vma, addr, rwc->arg)) { |
|
anon_vma_unlock_read(anon_vma); |
|
return; |
|
} |
|
if (rwc->done && rwc->done(page)) { |
|
anon_vma_unlock_read(anon_vma); |
|
return; |
|
} |
|
} |
|
anon_vma_unlock_read(anon_vma); |
|
} |
|
if (!search_new_forks++) |
|
goto again; |
|
} |
|
|
|
#ifdef CONFIG_MIGRATION |
|
void ksm_migrate_page(struct page *newpage, struct page *oldpage) |
|
{ |
|
struct stable_node *stable_node; |
|
|
|
VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage); |
|
VM_BUG_ON_PAGE(!PageLocked(newpage), newpage); |
|
VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage); |
|
|
|
stable_node = page_stable_node(newpage); |
|
if (stable_node) { |
|
VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage); |
|
stable_node->kpfn = page_to_pfn(newpage); |
|
/* |
|
* newpage->mapping was set in advance; now we need smp_wmb() |
|
* to make sure that the new stable_node->kpfn is visible |
|
* to get_ksm_page() before it can see that oldpage->mapping |
|
* has gone stale (or that PageSwapCache has been cleared). |
|
*/ |
|
smp_wmb(); |
|
set_page_stable_node(oldpage, NULL); |
|
} |
|
} |
|
#endif /* CONFIG_MIGRATION */ |
|
|
|
#ifdef CONFIG_MEMORY_HOTREMOVE |
|
static void wait_while_offlining(void) |
|
{ |
|
while (ksm_run & KSM_RUN_OFFLINE) { |
|
mutex_unlock(&ksm_thread_mutex); |
|
wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE), |
|
TASK_UNINTERRUPTIBLE); |
|
mutex_lock(&ksm_thread_mutex); |
|
} |
|
} |
|
|
|
static bool stable_node_dup_remove_range(struct stable_node *stable_node, |
|
unsigned long start_pfn, |
|
unsigned long end_pfn) |
|
{ |
|
if (stable_node->kpfn >= start_pfn && |
|
stable_node->kpfn < end_pfn) { |
|
/* |
|
* Don't get_ksm_page, page has already gone: |
|
* which is why we keep kpfn instead of page* |
|
*/ |
|
remove_node_from_stable_tree(stable_node); |
|
return true; |
|
} |
|
return false; |
|
} |
|
|
|
static bool stable_node_chain_remove_range(struct stable_node *stable_node, |
|
unsigned long start_pfn, |
|
unsigned long end_pfn, |
|
struct rb_root *root) |
|
{ |
|
struct stable_node *dup; |
|
struct hlist_node *hlist_safe; |
|
|
|
if (!is_stable_node_chain(stable_node)) { |
|
VM_BUG_ON(is_stable_node_dup(stable_node)); |
|
return stable_node_dup_remove_range(stable_node, start_pfn, |
|
end_pfn); |
|
} |
|
|
|
hlist_for_each_entry_safe(dup, hlist_safe, |
|
&stable_node->hlist, hlist_dup) { |
|
VM_BUG_ON(!is_stable_node_dup(dup)); |
|
stable_node_dup_remove_range(dup, start_pfn, end_pfn); |
|
} |
|
if (hlist_empty(&stable_node->hlist)) { |
|
free_stable_node_chain(stable_node, root); |
|
return true; /* notify caller that tree was rebalanced */ |
|
} else |
|
return false; |
|
} |
|
|
|
static void ksm_check_stable_tree(unsigned long start_pfn, |
|
unsigned long end_pfn) |
|
{ |
|
struct stable_node *stable_node, *next; |
|
struct rb_node *node; |
|
int nid; |
|
|
|
for (nid = 0; nid < ksm_nr_node_ids; nid++) { |
|
node = rb_first(root_stable_tree + nid); |
|
while (node) { |
|
stable_node = rb_entry(node, struct stable_node, node); |
|
if (stable_node_chain_remove_range(stable_node, |
|
start_pfn, end_pfn, |
|
root_stable_tree + |
|
nid)) |
|
node = rb_first(root_stable_tree + nid); |
|
else |
|
node = rb_next(node); |
|
cond_resched(); |
|
} |
|
} |
|
list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) { |
|
if (stable_node->kpfn >= start_pfn && |
|
stable_node->kpfn < end_pfn) |
|
remove_node_from_stable_tree(stable_node); |
|
cond_resched(); |
|
} |
|
} |
|
|
|
static int ksm_memory_callback(struct notifier_block *self, |
|
unsigned long action, void *arg) |
|
{ |
|
struct memory_notify *mn = arg; |
|
|
|
switch (action) { |
|
case MEM_GOING_OFFLINE: |
|
/* |
|
* Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items() |
|
* and remove_all_stable_nodes() while memory is going offline: |
|
* it is unsafe for them to touch the stable tree at this time. |
|
* But unmerge_ksm_pages(), rmap lookups and other entry points |
|
* which do not need the ksm_thread_mutex are all safe. |
|
*/ |
|
mutex_lock(&ksm_thread_mutex); |
|
ksm_run |= KSM_RUN_OFFLINE; |
|
mutex_unlock(&ksm_thread_mutex); |
|
break; |
|
|
|
case MEM_OFFLINE: |
|
/* |
|
* Most of the work is done by page migration; but there might |
|
* be a few stable_nodes left over, still pointing to struct |
|
* pages which have been offlined: prune those from the tree, |
|
* otherwise get_ksm_page() might later try to access a |
|
* non-existent struct page. |
|
*/ |
|
ksm_check_stable_tree(mn->start_pfn, |
|
mn->start_pfn + mn->nr_pages); |
|
fallthrough; |
|
case MEM_CANCEL_OFFLINE: |
|
mutex_lock(&ksm_thread_mutex); |
|
ksm_run &= ~KSM_RUN_OFFLINE; |
|
mutex_unlock(&ksm_thread_mutex); |
|
|
|
smp_mb(); /* wake_up_bit advises this */ |
|
wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE)); |
|
break; |
|
} |
|
return NOTIFY_OK; |
|
} |
|
#else |
|
static void wait_while_offlining(void) |
|
{ |
|
} |
|
#endif /* CONFIG_MEMORY_HOTREMOVE */ |
|
|
|
#ifdef CONFIG_SYSFS |
|
/* |
|
* This all compiles without CONFIG_SYSFS, but is a waste of space. |
|
*/ |
|
|
|
#define KSM_ATTR_RO(_name) \ |
|
static struct kobj_attribute _name##_attr = __ATTR_RO(_name) |
|
#define KSM_ATTR(_name) \ |
|
static struct kobj_attribute _name##_attr = \ |
|
__ATTR(_name, 0644, _name##_show, _name##_store) |
|
|
|
static ssize_t sleep_millisecs_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%u\n", ksm_thread_sleep_millisecs); |
|
} |
|
|
|
static ssize_t sleep_millisecs_store(struct kobject *kobj, |
|
struct kobj_attribute *attr, |
|
const char *buf, size_t count) |
|
{ |
|
unsigned int msecs; |
|
int err; |
|
|
|
err = kstrtouint(buf, 10, &msecs); |
|
if (err) |
|
return -EINVAL; |
|
|
|
ksm_thread_sleep_millisecs = msecs; |
|
wake_up_interruptible(&ksm_iter_wait); |
|
|
|
return count; |
|
} |
|
KSM_ATTR(sleep_millisecs); |
|
|
|
static ssize_t pages_to_scan_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%u\n", ksm_thread_pages_to_scan); |
|
} |
|
|
|
static ssize_t pages_to_scan_store(struct kobject *kobj, |
|
struct kobj_attribute *attr, |
|
const char *buf, size_t count) |
|
{ |
|
unsigned int nr_pages; |
|
int err; |
|
|
|
err = kstrtouint(buf, 10, &nr_pages); |
|
if (err) |
|
return -EINVAL; |
|
|
|
ksm_thread_pages_to_scan = nr_pages; |
|
|
|
return count; |
|
} |
|
KSM_ATTR(pages_to_scan); |
|
|
|
static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, |
|
char *buf) |
|
{ |
|
return sysfs_emit(buf, "%lu\n", ksm_run); |
|
} |
|
|
|
static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, |
|
const char *buf, size_t count) |
|
{ |
|
unsigned int flags; |
|
int err; |
|
|
|
err = kstrtouint(buf, 10, &flags); |
|
if (err) |
|
return -EINVAL; |
|
if (flags > KSM_RUN_UNMERGE) |
|
return -EINVAL; |
|
|
|
/* |
|
* KSM_RUN_MERGE sets ksmd running, and 0 stops it running. |
|
* KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, |
|
* breaking COW to free the pages_shared (but leaves mm_slots |
|
* on the list for when ksmd may be set running again). |
|
*/ |
|
|
|
mutex_lock(&ksm_thread_mutex); |
|
wait_while_offlining(); |
|
if (ksm_run != flags) { |
|
ksm_run = flags; |
|
if (flags & KSM_RUN_UNMERGE) { |
|
set_current_oom_origin(); |
|
err = unmerge_and_remove_all_rmap_items(); |
|
clear_current_oom_origin(); |
|
if (err) { |
|
ksm_run = KSM_RUN_STOP; |
|
count = err; |
|
} |
|
} |
|
} |
|
mutex_unlock(&ksm_thread_mutex); |
|
|
|
if (flags & KSM_RUN_MERGE) |
|
wake_up_interruptible(&ksm_thread_wait); |
|
|
|
return count; |
|
} |
|
KSM_ATTR(run); |
|
|
|
#ifdef CONFIG_NUMA |
|
static ssize_t merge_across_nodes_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes); |
|
} |
|
|
|
static ssize_t merge_across_nodes_store(struct kobject *kobj, |
|
struct kobj_attribute *attr, |
|
const char *buf, size_t count) |
|
{ |
|
int err; |
|
unsigned long knob; |
|
|
|
err = kstrtoul(buf, 10, &knob); |
|
if (err) |
|
return err; |
|
if (knob > 1) |
|
return -EINVAL; |
|
|
|
mutex_lock(&ksm_thread_mutex); |
|
wait_while_offlining(); |
|
if (ksm_merge_across_nodes != knob) { |
|
if (ksm_pages_shared || remove_all_stable_nodes()) |
|
err = -EBUSY; |
|
else if (root_stable_tree == one_stable_tree) { |
|
struct rb_root *buf; |
|
/* |
|
* This is the first time that we switch away from the |
|
* default of merging across nodes: must now allocate |
|
* a buffer to hold as many roots as may be needed. |
|
* Allocate stable and unstable together: |
|
* MAXSMP NODES_SHIFT 10 will use 16kB. |
|
*/ |
|
buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf), |
|
GFP_KERNEL); |
|
/* Let us assume that RB_ROOT is NULL is zero */ |
|
if (!buf) |
|
err = -ENOMEM; |
|
else { |
|
root_stable_tree = buf; |
|
root_unstable_tree = buf + nr_node_ids; |
|
/* Stable tree is empty but not the unstable */ |
|
root_unstable_tree[0] = one_unstable_tree[0]; |
|
} |
|
} |
|
if (!err) { |
|
ksm_merge_across_nodes = knob; |
|
ksm_nr_node_ids = knob ? 1 : nr_node_ids; |
|
} |
|
} |
|
mutex_unlock(&ksm_thread_mutex); |
|
|
|
return err ? err : count; |
|
} |
|
KSM_ATTR(merge_across_nodes); |
|
#endif |
|
|
|
static ssize_t use_zero_pages_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%u\n", ksm_use_zero_pages); |
|
} |
|
static ssize_t use_zero_pages_store(struct kobject *kobj, |
|
struct kobj_attribute *attr, |
|
const char *buf, size_t count) |
|
{ |
|
int err; |
|
bool value; |
|
|
|
err = kstrtobool(buf, &value); |
|
if (err) |
|
return -EINVAL; |
|
|
|
ksm_use_zero_pages = value; |
|
|
|
return count; |
|
} |
|
KSM_ATTR(use_zero_pages); |
|
|
|
static ssize_t max_page_sharing_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%u\n", ksm_max_page_sharing); |
|
} |
|
|
|
static ssize_t max_page_sharing_store(struct kobject *kobj, |
|
struct kobj_attribute *attr, |
|
const char *buf, size_t count) |
|
{ |
|
int err; |
|
int knob; |
|
|
|
err = kstrtoint(buf, 10, &knob); |
|
if (err) |
|
return err; |
|
/* |
|
* When a KSM page is created it is shared by 2 mappings. This |
|
* being a signed comparison, it implicitly verifies it's not |
|
* negative. |
|
*/ |
|
if (knob < 2) |
|
return -EINVAL; |
|
|
|
if (READ_ONCE(ksm_max_page_sharing) == knob) |
|
return count; |
|
|
|
mutex_lock(&ksm_thread_mutex); |
|
wait_while_offlining(); |
|
if (ksm_max_page_sharing != knob) { |
|
if (ksm_pages_shared || remove_all_stable_nodes()) |
|
err = -EBUSY; |
|
else |
|
ksm_max_page_sharing = knob; |
|
} |
|
mutex_unlock(&ksm_thread_mutex); |
|
|
|
return err ? err : count; |
|
} |
|
KSM_ATTR(max_page_sharing); |
|
|
|
static ssize_t pages_shared_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%lu\n", ksm_pages_shared); |
|
} |
|
KSM_ATTR_RO(pages_shared); |
|
|
|
static ssize_t pages_sharing_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%lu\n", ksm_pages_sharing); |
|
} |
|
KSM_ATTR_RO(pages_sharing); |
|
|
|
static ssize_t pages_unshared_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%lu\n", ksm_pages_unshared); |
|
} |
|
KSM_ATTR_RO(pages_unshared); |
|
|
|
static ssize_t pages_volatile_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
long ksm_pages_volatile; |
|
|
|
ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared |
|
- ksm_pages_sharing - ksm_pages_unshared; |
|
/* |
|
* It was not worth any locking to calculate that statistic, |
|
* but it might therefore sometimes be negative: conceal that. |
|
*/ |
|
if (ksm_pages_volatile < 0) |
|
ksm_pages_volatile = 0; |
|
return sysfs_emit(buf, "%ld\n", ksm_pages_volatile); |
|
} |
|
KSM_ATTR_RO(pages_volatile); |
|
|
|
static ssize_t stable_node_dups_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups); |
|
} |
|
KSM_ATTR_RO(stable_node_dups); |
|
|
|
static ssize_t stable_node_chains_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains); |
|
} |
|
KSM_ATTR_RO(stable_node_chains); |
|
|
|
static ssize_t |
|
stable_node_chains_prune_millisecs_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, |
|
char *buf) |
|
{ |
|
return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs); |
|
} |
|
|
|
static ssize_t |
|
stable_node_chains_prune_millisecs_store(struct kobject *kobj, |
|
struct kobj_attribute *attr, |
|
const char *buf, size_t count) |
|
{ |
|
unsigned int msecs; |
|
int err; |
|
|
|
err = kstrtouint(buf, 10, &msecs); |
|
if (err) |
|
return -EINVAL; |
|
|
|
ksm_stable_node_chains_prune_millisecs = msecs; |
|
|
|
return count; |
|
} |
|
KSM_ATTR(stable_node_chains_prune_millisecs); |
|
|
|
static ssize_t full_scans_show(struct kobject *kobj, |
|
struct kobj_attribute *attr, char *buf) |
|
{ |
|
return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr); |
|
} |
|
KSM_ATTR_RO(full_scans); |
|
|
|
static struct attribute *ksm_attrs[] = { |
|
&sleep_millisecs_attr.attr, |
|
&pages_to_scan_attr.attr, |
|
&run_attr.attr, |
|
&pages_shared_attr.attr, |
|
&pages_sharing_attr.attr, |
|
&pages_unshared_attr.attr, |
|
&pages_volatile_attr.attr, |
|
&full_scans_attr.attr, |
|
#ifdef CONFIG_NUMA |
|
&merge_across_nodes_attr.attr, |
|
#endif |
|
&max_page_sharing_attr.attr, |
|
&stable_node_chains_attr.attr, |
|
&stable_node_dups_attr.attr, |
|
&stable_node_chains_prune_millisecs_attr.attr, |
|
&use_zero_pages_attr.attr, |
|
NULL, |
|
}; |
|
|
|
static const struct attribute_group ksm_attr_group = { |
|
.attrs = ksm_attrs, |
|
.name = "ksm", |
|
}; |
|
#endif /* CONFIG_SYSFS */ |
|
|
|
static int __init ksm_init(void) |
|
{ |
|
struct task_struct *ksm_thread; |
|
int err; |
|
|
|
/* The correct value depends on page size and endianness */ |
|
zero_checksum = calc_checksum(ZERO_PAGE(0)); |
|
/* Default to false for backwards compatibility */ |
|
ksm_use_zero_pages = false; |
|
|
|
err = ksm_slab_init(); |
|
if (err) |
|
goto out; |
|
|
|
ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); |
|
if (IS_ERR(ksm_thread)) { |
|
pr_err("ksm: creating kthread failed\n"); |
|
err = PTR_ERR(ksm_thread); |
|
goto out_free; |
|
} |
|
|
|
#ifdef CONFIG_SYSFS |
|
err = sysfs_create_group(mm_kobj, &ksm_attr_group); |
|
if (err) { |
|
pr_err("ksm: register sysfs failed\n"); |
|
kthread_stop(ksm_thread); |
|
goto out_free; |
|
} |
|
#else |
|
ksm_run = KSM_RUN_MERGE; /* no way for user to start it */ |
|
|
|
#endif /* CONFIG_SYSFS */ |
|
|
|
#ifdef CONFIG_MEMORY_HOTREMOVE |
|
/* There is no significance to this priority 100 */ |
|
hotplug_memory_notifier(ksm_memory_callback, 100); |
|
#endif |
|
return 0; |
|
|
|
out_free: |
|
ksm_slab_free(); |
|
out: |
|
return err; |
|
} |
|
subsys_initcall(ksm_init);
|
|
|