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![Thomas Gleixner](/assets/img/avatar_default.png)
Add SPDX license identifiers to all files which: - Have no license information of any form - Have MODULE_LICENCE("GPL*") inside which was used in the initial scan/conversion to ignore the file These files fall under the project license, GPL v2 only. The resulting SPDX license identifier is: GPL-2.0-only Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
637 lines
18 KiB
C
637 lines
18 KiB
C
// 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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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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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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* 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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* 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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* 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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* zpool
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****************/
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#ifdef CONFIG_ZPOOL
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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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.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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* 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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/* 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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/* 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 = 0;
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return zhdr;
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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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* 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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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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/* First, try to find an unbuddied zbud page. */
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zhdr = NULL;
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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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/* 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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*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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spin_lock(&pool->lock);
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zhdr = handle_to_zbud_header(handle);
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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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/* Remove from existing buddy list */
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list_del(&zhdr->buddy);
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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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spin_unlock(&pool->lock);
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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()
|
|
* contains logic to delay freeing the page if the page is under reclaim,
|
|
* as indicated by the setting of the PG_reclaim flag on the underlying page.
|
|
*
|
|
* If all buddies in the zbud page are successfully evicted, then the
|
|
* zbud page can be freed.
|
|
*
|
|
* Returns: 0 if page is successfully freed, otherwise -EINVAL if there are
|
|
* no pages to evict or an eviction handler is not registered, -EAGAIN if
|
|
* the retry limit was hit.
|
|
*/
|
|
int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries)
|
|
{
|
|
int i, ret, freechunks;
|
|
struct zbud_header *zhdr;
|
|
unsigned long first_handle = 0, last_handle = 0;
|
|
|
|
spin_lock(&pool->lock);
|
|
if (!pool->ops || !pool->ops->evict || list_empty(&pool->lru) ||
|
|
retries == 0) {
|
|
spin_unlock(&pool->lock);
|
|
return -EINVAL;
|
|
}
|
|
for (i = 0; i < retries; i++) {
|
|
zhdr = list_last_entry(&pool->lru, struct zbud_header, lru);
|
|
list_del(&zhdr->lru);
|
|
list_del(&zhdr->buddy);
|
|
/* Protect zbud page against free */
|
|
zhdr->under_reclaim = true;
|
|
/*
|
|
* We need encode the handles before unlocking, since we can
|
|
* race with free that will set (first|last)_chunks to 0
|
|
*/
|
|
first_handle = 0;
|
|
last_handle = 0;
|
|
if (zhdr->first_chunks)
|
|
first_handle = encode_handle(zhdr, FIRST);
|
|
if (zhdr->last_chunks)
|
|
last_handle = encode_handle(zhdr, LAST);
|
|
spin_unlock(&pool->lock);
|
|
|
|
/* Issue the eviction callback(s) */
|
|
if (first_handle) {
|
|
ret = pool->ops->evict(pool, first_handle);
|
|
if (ret)
|
|
goto next;
|
|
}
|
|
if (last_handle) {
|
|
ret = pool->ops->evict(pool, last_handle);
|
|
if (ret)
|
|
goto next;
|
|
}
|
|
next:
|
|
spin_lock(&pool->lock);
|
|
zhdr->under_reclaim = false;
|
|
if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
|
|
/*
|
|
* Both buddies are now free, free the zbud page and
|
|
* return success.
|
|
*/
|
|
free_zbud_page(zhdr);
|
|
pool->pages_nr--;
|
|
spin_unlock(&pool->lock);
|
|
return 0;
|
|
} else if (zhdr->first_chunks == 0 ||
|
|
zhdr->last_chunks == 0) {
|
|
/* add to unbuddied list */
|
|
freechunks = num_free_chunks(zhdr);
|
|
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 <sjennings@variantweb.net>");
|
|
MODULE_DESCRIPTION("Buddy Allocator for Compressed Pages");
|