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637 lines
18 KiB
637 lines
18 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* zbud.c |
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* |
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* Copyright (C) 2013, Seth Jennings, IBM |
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* |
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* Concepts based on zcache internal zbud allocator by Dan Magenheimer. |
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* |
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* zbud is an special purpose allocator for storing compressed pages. Contrary |
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* to what its name may suggest, zbud is not a buddy allocator, but rather an |
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* allocator that "buddies" two compressed pages together in a single memory |
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* page. |
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* |
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* While this design limits storage density, it has simple and deterministic |
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* reclaim properties that make it preferable to a higher density approach when |
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* reclaim will be used. |
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* |
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* zbud works by storing compressed pages, or "zpages", together in pairs in a |
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* single memory page called a "zbud page". The first buddy is "left |
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* justified" at the beginning of the zbud page, and the last buddy is "right |
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* justified" at the end of the zbud page. The benefit is that if either |
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* buddy is freed, the freed buddy space, coalesced with whatever slack space |
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* that existed between the buddies, results in the largest possible free region |
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* within the zbud page. |
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* |
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* zbud also provides an attractive lower bound on density. The ratio of zpages |
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* to zbud pages can not be less than 1. This ensures that zbud can never "do |
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* harm" by using more pages to store zpages than the uncompressed zpages would |
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* have used on their own. |
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* |
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* zbud pages are divided into "chunks". The size of the chunks is fixed at |
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* compile time and determined by NCHUNKS_ORDER below. Dividing zbud pages |
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* into chunks allows organizing unbuddied zbud pages into a manageable number |
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* of unbuddied lists according to the number of free chunks available in the |
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* zbud page. |
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* |
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* The zbud API differs from that of conventional allocators in that the |
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* allocation function, zbud_alloc(), returns an opaque handle to the user, |
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* not a dereferenceable pointer. The user must map the handle using |
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* zbud_map() in order to get a usable pointer by which to access the |
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* allocation data and unmap the handle with zbud_unmap() when operations |
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* on the allocation data are complete. |
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*/ |
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|
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
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|
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#include <linux/atomic.h> |
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#include <linux/list.h> |
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#include <linux/mm.h> |
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#include <linux/module.h> |
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#include <linux/preempt.h> |
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#include <linux/slab.h> |
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#include <linux/spinlock.h> |
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#include <linux/zbud.h> |
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#include <linux/zpool.h> |
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|
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/***************** |
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* Structures |
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*****************/ |
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/* |
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* NCHUNKS_ORDER determines the internal allocation granularity, effectively |
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* adjusting internal fragmentation. It also determines the number of |
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* freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the |
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* allocation granularity will be in chunks of size PAGE_SIZE/64. As one chunk |
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* in allocated page is occupied by zbud header, NCHUNKS will be calculated to |
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* 63 which shows the max number of free chunks in zbud page, also there will be |
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* 63 freelists per pool. |
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*/ |
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#define NCHUNKS_ORDER 6 |
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#define CHUNK_SHIFT (PAGE_SHIFT - NCHUNKS_ORDER) |
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#define CHUNK_SIZE (1 << CHUNK_SHIFT) |
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#define ZHDR_SIZE_ALIGNED CHUNK_SIZE |
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#define NCHUNKS ((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT) |
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|
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/** |
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* struct zbud_pool - stores metadata for each zbud pool |
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* @lock: protects all pool fields and first|last_chunk fields of any |
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* zbud page in the pool |
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* @unbuddied: array of lists tracking zbud pages that only contain one buddy; |
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* the lists each zbud page is added to depends on the size of |
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* its free region. |
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* @buddied: list tracking the zbud pages that contain two buddies; |
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* these zbud pages are full |
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* @lru: list tracking the zbud pages in LRU order by most recently |
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* added buddy. |
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* @pages_nr: number of zbud pages in the pool. |
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* @ops: pointer to a structure of user defined operations specified at |
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* pool creation time. |
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* |
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* This structure is allocated at pool creation time and maintains metadata |
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* pertaining to a particular zbud pool. |
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*/ |
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struct zbud_pool { |
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spinlock_t lock; |
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struct list_head unbuddied[NCHUNKS]; |
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struct list_head buddied; |
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struct list_head lru; |
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u64 pages_nr; |
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const struct zbud_ops *ops; |
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#ifdef CONFIG_ZPOOL |
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struct zpool *zpool; |
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const struct zpool_ops *zpool_ops; |
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#endif |
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}; |
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|
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/* |
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* struct zbud_header - zbud page metadata occupying the first chunk of each |
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* zbud page. |
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* @buddy: links the zbud page into the unbuddied/buddied lists in the pool |
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* @lru: links the zbud page into the lru list in the pool |
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* @first_chunks: the size of the first buddy in chunks, 0 if free |
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* @last_chunks: the size of the last buddy in chunks, 0 if free |
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*/ |
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struct zbud_header { |
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struct list_head buddy; |
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struct list_head lru; |
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unsigned int first_chunks; |
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unsigned int last_chunks; |
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bool under_reclaim; |
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}; |
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|
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/***************** |
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* zpool |
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****************/ |
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#ifdef CONFIG_ZPOOL |
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|
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static int zbud_zpool_evict(struct zbud_pool *pool, unsigned long handle) |
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{ |
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if (pool->zpool && pool->zpool_ops && pool->zpool_ops->evict) |
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return pool->zpool_ops->evict(pool->zpool, handle); |
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else |
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return -ENOENT; |
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} |
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static const struct zbud_ops zbud_zpool_ops = { |
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.evict = zbud_zpool_evict |
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}; |
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static void *zbud_zpool_create(const char *name, gfp_t gfp, |
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const struct zpool_ops *zpool_ops, |
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struct zpool *zpool) |
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{ |
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struct zbud_pool *pool; |
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pool = zbud_create_pool(gfp, zpool_ops ? &zbud_zpool_ops : NULL); |
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if (pool) { |
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pool->zpool = zpool; |
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pool->zpool_ops = zpool_ops; |
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} |
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return pool; |
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} |
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static void zbud_zpool_destroy(void *pool) |
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{ |
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zbud_destroy_pool(pool); |
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} |
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static int zbud_zpool_malloc(void *pool, size_t size, gfp_t gfp, |
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unsigned long *handle) |
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{ |
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return zbud_alloc(pool, size, gfp, handle); |
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} |
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static void zbud_zpool_free(void *pool, unsigned long handle) |
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{ |
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zbud_free(pool, handle); |
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} |
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static int zbud_zpool_shrink(void *pool, unsigned int pages, |
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unsigned int *reclaimed) |
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{ |
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unsigned int total = 0; |
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int ret = -EINVAL; |
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while (total < pages) { |
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ret = zbud_reclaim_page(pool, 8); |
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if (ret < 0) |
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break; |
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total++; |
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} |
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if (reclaimed) |
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*reclaimed = total; |
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return ret; |
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} |
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static void *zbud_zpool_map(void *pool, unsigned long handle, |
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enum zpool_mapmode mm) |
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{ |
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return zbud_map(pool, handle); |
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} |
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static void zbud_zpool_unmap(void *pool, unsigned long handle) |
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{ |
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zbud_unmap(pool, handle); |
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} |
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static u64 zbud_zpool_total_size(void *pool) |
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{ |
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return zbud_get_pool_size(pool) * PAGE_SIZE; |
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} |
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static struct zpool_driver zbud_zpool_driver = { |
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.type = "zbud", |
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.sleep_mapped = true, |
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.owner = THIS_MODULE, |
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.create = zbud_zpool_create, |
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.destroy = zbud_zpool_destroy, |
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.malloc = zbud_zpool_malloc, |
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.free = zbud_zpool_free, |
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.shrink = zbud_zpool_shrink, |
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.map = zbud_zpool_map, |
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.unmap = zbud_zpool_unmap, |
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.total_size = zbud_zpool_total_size, |
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}; |
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MODULE_ALIAS("zpool-zbud"); |
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#endif /* CONFIG_ZPOOL */ |
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|
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/***************** |
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* Helpers |
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*****************/ |
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/* Just to make the code easier to read */ |
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enum buddy { |
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FIRST, |
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LAST |
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}; |
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|
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/* Converts an allocation size in bytes to size in zbud chunks */ |
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static int size_to_chunks(size_t size) |
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{ |
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return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT; |
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} |
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#define for_each_unbuddied_list(_iter, _begin) \ |
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for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++) |
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|
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/* Initializes the zbud header of a newly allocated zbud page */ |
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static struct zbud_header *init_zbud_page(struct page *page) |
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{ |
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struct zbud_header *zhdr = page_address(page); |
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zhdr->first_chunks = 0; |
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zhdr->last_chunks = 0; |
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INIT_LIST_HEAD(&zhdr->buddy); |
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INIT_LIST_HEAD(&zhdr->lru); |
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zhdr->under_reclaim = false; |
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return zhdr; |
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} |
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|
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/* Resets the struct page fields and frees the page */ |
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static void free_zbud_page(struct zbud_header *zhdr) |
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{ |
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__free_page(virt_to_page(zhdr)); |
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} |
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/* |
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* Encodes the handle of a particular buddy within a zbud page |
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* Pool lock should be held as this function accesses first|last_chunks |
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*/ |
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static unsigned long encode_handle(struct zbud_header *zhdr, enum buddy bud) |
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{ |
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unsigned long handle; |
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/* |
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* For now, the encoded handle is actually just the pointer to the data |
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* but this might not always be the case. A little information hiding. |
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* Add CHUNK_SIZE to the handle if it is the first allocation to jump |
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* over the zbud header in the first chunk. |
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*/ |
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handle = (unsigned long)zhdr; |
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if (bud == FIRST) |
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/* skip over zbud header */ |
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handle += ZHDR_SIZE_ALIGNED; |
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else /* bud == LAST */ |
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handle += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT); |
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return handle; |
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} |
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/* Returns the zbud page where a given handle is stored */ |
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static struct zbud_header *handle_to_zbud_header(unsigned long handle) |
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{ |
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return (struct zbud_header *)(handle & PAGE_MASK); |
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} |
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/* Returns the number of free chunks in a zbud page */ |
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static int num_free_chunks(struct zbud_header *zhdr) |
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{ |
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/* |
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* Rather than branch for different situations, just use the fact that |
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* free buddies have a length of zero to simplify everything. |
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*/ |
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return NCHUNKS - zhdr->first_chunks - zhdr->last_chunks; |
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} |
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|
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/***************** |
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* API Functions |
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*****************/ |
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/** |
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* zbud_create_pool() - create a new zbud pool |
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* @gfp: gfp flags when allocating the zbud pool structure |
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* @ops: user-defined operations for the zbud pool |
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* |
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* Return: pointer to the new zbud pool or NULL if the metadata allocation |
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* failed. |
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*/ |
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struct zbud_pool *zbud_create_pool(gfp_t gfp, const struct zbud_ops *ops) |
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{ |
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struct zbud_pool *pool; |
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int i; |
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pool = kzalloc(sizeof(struct zbud_pool), gfp); |
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if (!pool) |
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return NULL; |
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spin_lock_init(&pool->lock); |
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for_each_unbuddied_list(i, 0) |
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INIT_LIST_HEAD(&pool->unbuddied[i]); |
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INIT_LIST_HEAD(&pool->buddied); |
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INIT_LIST_HEAD(&pool->lru); |
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pool->pages_nr = 0; |
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pool->ops = ops; |
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return pool; |
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} |
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/** |
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* zbud_destroy_pool() - destroys an existing zbud pool |
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* @pool: the zbud pool to be destroyed |
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* |
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* The pool should be emptied before this function is called. |
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*/ |
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void zbud_destroy_pool(struct zbud_pool *pool) |
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{ |
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kfree(pool); |
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} |
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/** |
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* zbud_alloc() - allocates a region of a given size |
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* @pool: zbud pool from which to allocate |
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* @size: size in bytes of the desired allocation |
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* @gfp: gfp flags used if the pool needs to grow |
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* @handle: handle of the new allocation |
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* |
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* This function will attempt to find a free region in the pool large enough to |
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* satisfy the allocation request. A search of the unbuddied lists is |
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* performed first. If no suitable free region is found, then a new page is |
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* allocated and added to the pool to satisfy the request. |
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* |
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* gfp should not set __GFP_HIGHMEM as highmem pages cannot be used |
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* as zbud pool pages. |
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* |
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* Return: 0 if success and handle is set, otherwise -EINVAL if the size or |
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* gfp arguments are invalid or -ENOMEM if the pool was unable to allocate |
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* a new page. |
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*/ |
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int zbud_alloc(struct zbud_pool *pool, size_t size, gfp_t gfp, |
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unsigned long *handle) |
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{ |
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int chunks, i, freechunks; |
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struct zbud_header *zhdr = NULL; |
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enum buddy bud; |
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struct page *page; |
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|
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if (!size || (gfp & __GFP_HIGHMEM)) |
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return -EINVAL; |
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if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE) |
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return -ENOSPC; |
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chunks = size_to_chunks(size); |
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spin_lock(&pool->lock); |
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|
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/* First, try to find an unbuddied zbud page. */ |
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for_each_unbuddied_list(i, chunks) { |
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if (!list_empty(&pool->unbuddied[i])) { |
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zhdr = list_first_entry(&pool->unbuddied[i], |
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struct zbud_header, buddy); |
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list_del(&zhdr->buddy); |
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if (zhdr->first_chunks == 0) |
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bud = FIRST; |
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else |
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bud = LAST; |
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goto found; |
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} |
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} |
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/* Couldn't find unbuddied zbud page, create new one */ |
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spin_unlock(&pool->lock); |
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page = alloc_page(gfp); |
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if (!page) |
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return -ENOMEM; |
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spin_lock(&pool->lock); |
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pool->pages_nr++; |
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zhdr = init_zbud_page(page); |
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bud = FIRST; |
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found: |
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if (bud == FIRST) |
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zhdr->first_chunks = chunks; |
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else |
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zhdr->last_chunks = chunks; |
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if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0) { |
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/* Add to unbuddied list */ |
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freechunks = num_free_chunks(zhdr); |
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list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); |
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} else { |
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/* Add to buddied list */ |
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list_add(&zhdr->buddy, &pool->buddied); |
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} |
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|
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/* Add/move zbud page to beginning of LRU */ |
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if (!list_empty(&zhdr->lru)) |
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list_del(&zhdr->lru); |
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list_add(&zhdr->lru, &pool->lru); |
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|
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*handle = encode_handle(zhdr, bud); |
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spin_unlock(&pool->lock); |
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return 0; |
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} |
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/** |
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* zbud_free() - frees the allocation associated with the given handle |
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* @pool: pool in which the allocation resided |
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* @handle: handle associated with the allocation returned by zbud_alloc() |
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* |
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* In the case that the zbud page in which the allocation resides is under |
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* reclaim, as indicated by the PG_reclaim flag being set, this function |
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* only sets the first|last_chunks to 0. The page is actually freed |
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* once both buddies are evicted (see zbud_reclaim_page() below). |
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*/ |
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void zbud_free(struct zbud_pool *pool, unsigned long handle) |
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{ |
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struct zbud_header *zhdr; |
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int freechunks; |
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|
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spin_lock(&pool->lock); |
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zhdr = handle_to_zbud_header(handle); |
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|
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/* If first buddy, handle will be page aligned */ |
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if ((handle - ZHDR_SIZE_ALIGNED) & ~PAGE_MASK) |
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zhdr->last_chunks = 0; |
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else |
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zhdr->first_chunks = 0; |
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if (zhdr->under_reclaim) { |
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/* zbud page is under reclaim, reclaim will free */ |
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spin_unlock(&pool->lock); |
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return; |
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} |
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|
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/* Remove from existing buddy list */ |
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list_del(&zhdr->buddy); |
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|
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if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) { |
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/* zbud page is empty, free */ |
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list_del(&zhdr->lru); |
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free_zbud_page(zhdr); |
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pool->pages_nr--; |
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} else { |
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/* Add to unbuddied list */ |
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freechunks = num_free_chunks(zhdr); |
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list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); |
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} |
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|
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spin_unlock(&pool->lock); |
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} |
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|
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/** |
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* zbud_reclaim_page() - evicts allocations from a pool page and frees it |
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* @pool: pool from which a page will attempt to be evicted |
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* @retries: number of pages on the LRU list for which eviction will |
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* be attempted before failing |
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* |
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* zbud reclaim is different from normal system reclaim in that the reclaim is |
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* done from the bottom, up. This is because only the bottom layer, zbud, has |
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* information on how the allocations are organized within each zbud page. This |
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* has the potential to create interesting locking situations between zbud and |
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* the user, however. |
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* |
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* To avoid these, this is how zbud_reclaim_page() should be called: |
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* |
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* The user detects a page should be reclaimed and calls zbud_reclaim_page(). |
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* zbud_reclaim_page() will remove a zbud page from the pool LRU list and call |
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* the user-defined eviction handler with the pool and handle as arguments. |
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* |
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* If the handle can not be evicted, the eviction handler should return |
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* non-zero. zbud_reclaim_page() will add the zbud page back to the |
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* appropriate list and try the next zbud page on the LRU up to |
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* a user defined number of retries. |
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* |
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* If the handle is successfully evicted, the eviction handler should |
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* return 0 _and_ should have called zbud_free() on the handle. zbud_free() |
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* contains logic to delay freeing the page if the page is under reclaim, |
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* as indicated by the setting of the PG_reclaim flag on the underlying page. |
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* |
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* If all buddies in the zbud page are successfully evicted, then the |
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* zbud page can be freed. |
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* |
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* Returns: 0 if page is successfully freed, otherwise -EINVAL if there are |
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* no pages to evict or an eviction handler is not registered, -EAGAIN if |
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* the retry limit was hit. |
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*/ |
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int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries) |
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{ |
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int i, ret, freechunks; |
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struct zbud_header *zhdr; |
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unsigned long first_handle = 0, last_handle = 0; |
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|
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spin_lock(&pool->lock); |
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if (!pool->ops || !pool->ops->evict || list_empty(&pool->lru) || |
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retries == 0) { |
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spin_unlock(&pool->lock); |
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return -EINVAL; |
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} |
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for (i = 0; i < retries; i++) { |
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zhdr = list_last_entry(&pool->lru, struct zbud_header, lru); |
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list_del(&zhdr->lru); |
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list_del(&zhdr->buddy); |
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/* Protect zbud page against free */ |
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zhdr->under_reclaim = true; |
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/* |
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* We need encode the handles before unlocking, since we can |
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* race with free that will set (first|last)_chunks to 0 |
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*/ |
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first_handle = 0; |
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last_handle = 0; |
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if (zhdr->first_chunks) |
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first_handle = encode_handle(zhdr, FIRST); |
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if (zhdr->last_chunks) |
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last_handle = encode_handle(zhdr, LAST); |
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spin_unlock(&pool->lock); |
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|
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/* Issue the eviction callback(s) */ |
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if (first_handle) { |
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ret = pool->ops->evict(pool, first_handle); |
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if (ret) |
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goto next; |
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} |
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if (last_handle) { |
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ret = pool->ops->evict(pool, last_handle); |
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if (ret) |
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goto next; |
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} |
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next: |
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spin_lock(&pool->lock); |
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zhdr->under_reclaim = false; |
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if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) { |
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/* |
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* Both buddies are now free, free the zbud page and |
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* return success. |
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*/ |
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free_zbud_page(zhdr); |
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pool->pages_nr--; |
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spin_unlock(&pool->lock); |
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return 0; |
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} else if (zhdr->first_chunks == 0 || |
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zhdr->last_chunks == 0) { |
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/* add to unbuddied list */ |
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freechunks = num_free_chunks(zhdr); |
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list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); |
|
} else { |
|
/* add to buddied list */ |
|
list_add(&zhdr->buddy, &pool->buddied); |
|
} |
|
|
|
/* add to beginning of LRU */ |
|
list_add(&zhdr->lru, &pool->lru); |
|
} |
|
spin_unlock(&pool->lock); |
|
return -EAGAIN; |
|
} |
|
|
|
/** |
|
* zbud_map() - maps the allocation associated with the given handle |
|
* @pool: pool in which the allocation resides |
|
* @handle: handle associated with the allocation to be mapped |
|
* |
|
* While trivial for zbud, the mapping functions for others allocators |
|
* implementing this allocation API could have more complex information encoded |
|
* in the handle and could create temporary mappings to make the data |
|
* accessible to the user. |
|
* |
|
* Returns: a pointer to the mapped allocation |
|
*/ |
|
void *zbud_map(struct zbud_pool *pool, unsigned long handle) |
|
{ |
|
return (void *)(handle); |
|
} |
|
|
|
/** |
|
* zbud_unmap() - maps the allocation associated with the given handle |
|
* @pool: pool in which the allocation resides |
|
* @handle: handle associated with the allocation to be unmapped |
|
*/ |
|
void zbud_unmap(struct zbud_pool *pool, unsigned long handle) |
|
{ |
|
} |
|
|
|
/** |
|
* zbud_get_pool_size() - gets the zbud pool size in pages |
|
* @pool: pool whose size is being queried |
|
* |
|
* Returns: size in pages of the given pool. The pool lock need not be |
|
* taken to access pages_nr. |
|
*/ |
|
u64 zbud_get_pool_size(struct zbud_pool *pool) |
|
{ |
|
return pool->pages_nr; |
|
} |
|
|
|
static int __init init_zbud(void) |
|
{ |
|
/* Make sure the zbud header will fit in one chunk */ |
|
BUILD_BUG_ON(sizeof(struct zbud_header) > ZHDR_SIZE_ALIGNED); |
|
pr_info("loaded\n"); |
|
|
|
#ifdef CONFIG_ZPOOL |
|
zpool_register_driver(&zbud_zpool_driver); |
|
#endif |
|
|
|
return 0; |
|
} |
|
|
|
static void __exit exit_zbud(void) |
|
{ |
|
#ifdef CONFIG_ZPOOL |
|
zpool_unregister_driver(&zbud_zpool_driver); |
|
#endif |
|
|
|
pr_info("unloaded\n"); |
|
} |
|
|
|
module_init(init_zbud); |
|
module_exit(exit_zbud); |
|
|
|
MODULE_LICENSE("GPL"); |
|
MODULE_AUTHOR("Seth Jennings <[email protected]>"); |
|
MODULE_DESCRIPTION("Buddy Allocator for Compressed Pages");
|
|
|