+++ /dev/null
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * zbud.c
- *
- * Copyright (C) 2013, Seth Jennings, IBM
- *
- * Concepts based on zcache internal zbud allocator by Dan Magenheimer.
- *
- * zbud is an special purpose allocator for storing compressed pages. Contrary
- * to what its name may suggest, zbud is not a buddy allocator, but rather an
- * allocator that "buddies" two compressed pages together in a single memory
- * page.
- *
- * While this design limits storage density, it has simple and deterministic
- * reclaim properties that make it preferable to a higher density approach when
- * reclaim will be used.
- *
- * zbud works by storing compressed pages, or "zpages", together in pairs in a
- * single memory page called a "zbud page". The first buddy is "left
- * justified" at the beginning of the zbud page, and the last buddy is "right
- * justified" at the end of the zbud page. The benefit is that if either
- * buddy is freed, the freed buddy space, coalesced with whatever slack space
- * that existed between the buddies, results in the largest possible free region
- * within the zbud page.
- *
- * zbud also provides an attractive lower bound on density. The ratio of zpages
- * to zbud pages can not be less than 1. This ensures that zbud can never "do
- * harm" by using more pages to store zpages than the uncompressed zpages would
- * have used on their own.
- *
- * zbud pages are divided into "chunks". The size of the chunks is fixed at
- * compile time and determined by NCHUNKS_ORDER below. Dividing zbud pages
- * into chunks allows organizing unbuddied zbud pages into a manageable number
- * of unbuddied lists according to the number of free chunks available in the
- * zbud page.
- *
- * The zbud API differs from that of conventional allocators in that the
- * allocation function, zbud_alloc(), returns an opaque handle to the user,
- * not a dereferenceable pointer. The user must map the handle using
- * zbud_map() in order to get a usable pointer by which to access the
- * allocation data and unmap the handle with zbud_unmap() when operations
- * on the allocation data are complete.
- */
-
-#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
-
-#include <linux/atomic.h>
-#include <linux/list.h>
-#include <linux/mm.h>
-#include <linux/module.h>
-#include <linux/preempt.h>
-#include <linux/slab.h>
-#include <linux/spinlock.h>
-#include <linux/zpool.h>
-
-/*****************
- * Structures
-*****************/
-/*
- * NCHUNKS_ORDER determines the internal allocation granularity, effectively
- * adjusting internal fragmentation. It also determines the number of
- * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the
- * allocation granularity will be in chunks of size PAGE_SIZE/64. As one chunk
- * in allocated page is occupied by zbud header, NCHUNKS will be calculated to
- * 63 which shows the max number of free chunks in zbud page, also there will be
- * 63 freelists per pool.
- */
-#define NCHUNKS_ORDER 6
-
-#define CHUNK_SHIFT (PAGE_SHIFT - NCHUNKS_ORDER)
-#define CHUNK_SIZE (1 << CHUNK_SHIFT)
-#define ZHDR_SIZE_ALIGNED CHUNK_SIZE
-#define NCHUNKS ((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT)
-
-struct zbud_pool;
-
-/**
- * struct zbud_pool - stores metadata for each zbud pool
- * @lock: protects all pool fields and first|last_chunk fields of any
- * zbud page in the pool
- * @unbuddied: array of lists tracking zbud pages that only contain one buddy;
- * the lists each zbud page is added to depends on the size of
- * its free region.
- * @buddied: list tracking the zbud pages that contain two buddies;
- * these zbud pages are full
- * @pages_nr: number of zbud pages in the pool.
- *
- * This structure is allocated at pool creation time and maintains metadata
- * pertaining to a particular zbud pool.
- */
-struct zbud_pool {
- spinlock_t lock;
- union {
- /*
- * Reuse unbuddied[0] as buddied on the ground that
- * unbuddied[0] is unused.
- */
- struct list_head buddied;
- struct list_head unbuddied[NCHUNKS];
- };
- u64 pages_nr;
-};
-
-/*
- * struct zbud_header - zbud page metadata occupying the first chunk of each
- * zbud page.
- * @buddy: links the zbud page into the unbuddied/buddied lists in the pool
- * @first_chunks: the size of the first buddy in chunks, 0 if free
- * @last_chunks: the size of the last buddy in chunks, 0 if free
- */
-struct zbud_header {
- struct list_head buddy;
- unsigned int first_chunks;
- unsigned int last_chunks;
-};
-
-/*****************
- * Helpers
-*****************/
-/* Just to make the code easier to read */
-enum buddy {
- FIRST,
- LAST
-};
-
-/* Converts an allocation size in bytes to size in zbud chunks */
-static int size_to_chunks(size_t size)
-{
- return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
-}
-
-#define for_each_unbuddied_list(_iter, _begin) \
- for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
-
-/* Initializes the zbud header of a newly allocated zbud page */
-static struct zbud_header *init_zbud_page(struct page *page)
-{
- struct zbud_header *zhdr = page_address(page);
- zhdr->first_chunks = 0;
- zhdr->last_chunks = 0;
- INIT_LIST_HEAD(&zhdr->buddy);
- return zhdr;
-}
-
-/* Resets the struct page fields and frees the page */
-static void free_zbud_page(struct zbud_header *zhdr)
-{
- __free_page(virt_to_page(zhdr));
-}
-
-/*
- * Encodes the handle of a particular buddy within a zbud page
- * Pool lock should be held as this function accesses first|last_chunks
- */
-static unsigned long encode_handle(struct zbud_header *zhdr, enum buddy bud)
-{
- unsigned long handle;
-
- /*
- * For now, the encoded handle is actually just the pointer to the data
- * but this might not always be the case. A little information hiding.
- * Add CHUNK_SIZE to the handle if it is the first allocation to jump
- * over the zbud header in the first chunk.
- */
- handle = (unsigned long)zhdr;
- if (bud == FIRST)
- /* skip over zbud header */
- handle += ZHDR_SIZE_ALIGNED;
- else /* bud == LAST */
- handle += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
- return handle;
-}
-
-/* Returns the zbud page where a given handle is stored */
-static struct zbud_header *handle_to_zbud_header(unsigned long handle)
-{
- return (struct zbud_header *)(handle & PAGE_MASK);
-}
-
-/* Returns the number of free chunks in a zbud page */
-static int num_free_chunks(struct zbud_header *zhdr)
-{
- /*
- * Rather than branch for different situations, just use the fact that
- * free buddies have a length of zero to simplify everything.
- */
- return NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
-}
-
-/*****************
- * API Functions
-*****************/
-/**
- * zbud_create_pool() - create a new zbud pool
- * @gfp: gfp flags when allocating the zbud pool structure
- *
- * Return: pointer to the new zbud pool or NULL if the metadata allocation
- * failed.
- */
-static struct zbud_pool *zbud_create_pool(gfp_t gfp)
-{
- struct zbud_pool *pool;
- int i;
-
- pool = kzalloc(sizeof(struct zbud_pool), gfp);
- if (!pool)
- return NULL;
- spin_lock_init(&pool->lock);
- for_each_unbuddied_list(i, 0)
- INIT_LIST_HEAD(&pool->unbuddied[i]);
- INIT_LIST_HEAD(&pool->buddied);
- pool->pages_nr = 0;
- return pool;
-}
-
-/**
- * zbud_destroy_pool() - destroys an existing zbud pool
- * @pool: the zbud pool to be destroyed
- *
- * The pool should be emptied before this function is called.
- */
-static void zbud_destroy_pool(struct zbud_pool *pool)
-{
- kfree(pool);
-}
-
-/**
- * zbud_alloc() - allocates a region of a given size
- * @pool: zbud pool from which to allocate
- * @size: size in bytes of the desired allocation
- * @gfp: gfp flags used if the pool needs to grow
- * @handle: handle of the new allocation
- *
- * This function will attempt to find a free region in the pool large enough to
- * satisfy the allocation request. A search of the unbuddied lists is
- * performed first. If no suitable free region is found, then a new page is
- * allocated and added to the pool to satisfy the request.
- *
- * gfp should not set __GFP_HIGHMEM as highmem pages cannot be used
- * as zbud pool pages.
- *
- * Return: 0 if success and handle is set, otherwise -EINVAL if the size or
- * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
- * a new page.
- */
-static int zbud_alloc(struct zbud_pool *pool, size_t size, gfp_t gfp,
- unsigned long *handle)
-{
- int chunks, i, freechunks;
- struct zbud_header *zhdr = NULL;
- enum buddy bud;
- struct page *page;
-
- if (!size || (gfp & __GFP_HIGHMEM))
- return -EINVAL;
- if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
- return -ENOSPC;
- chunks = size_to_chunks(size);
- spin_lock(&pool->lock);
-
- /* First, try to find an unbuddied zbud page. */
- for_each_unbuddied_list(i, chunks) {
- if (!list_empty(&pool->unbuddied[i])) {
- zhdr = list_first_entry(&pool->unbuddied[i],
- struct zbud_header, buddy);
- list_del(&zhdr->buddy);
- if (zhdr->first_chunks == 0)
- bud = FIRST;
- else
- bud = LAST;
- goto found;
- }
- }
-
- /* Couldn't find unbuddied zbud page, create new one */
- spin_unlock(&pool->lock);
- page = alloc_page(gfp);
- if (!page)
- return -ENOMEM;
- spin_lock(&pool->lock);
- pool->pages_nr++;
- zhdr = init_zbud_page(page);
- bud = FIRST;
-
-found:
- if (bud == FIRST)
- zhdr->first_chunks = chunks;
- else
- zhdr->last_chunks = chunks;
-
- 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);
- }
-
- *handle = encode_handle(zhdr, bud);
- spin_unlock(&pool->lock);
-
- return 0;
-}
-
-/**
- * zbud_free() - frees the allocation associated with the given handle
- * @pool: pool in which the allocation resided
- * @handle: handle associated with the allocation returned by zbud_alloc()
- */
-static void zbud_free(struct zbud_pool *pool, unsigned long handle)
-{
- struct zbud_header *zhdr;
- int freechunks;
-
- spin_lock(&pool->lock);
- zhdr = handle_to_zbud_header(handle);
-
- /* If first buddy, handle will be page aligned */
- if ((handle - ZHDR_SIZE_ALIGNED) & ~PAGE_MASK)
- zhdr->last_chunks = 0;
- else
- zhdr->first_chunks = 0;
-
- /* Remove from existing buddy list */
- list_del(&zhdr->buddy);
-
- if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
- /* zbud page is empty, free */
- free_zbud_page(zhdr);
- pool->pages_nr--;
- } else {
- /* Add to unbuddied list */
- freechunks = num_free_chunks(zhdr);
- list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
- }
-
- spin_unlock(&pool->lock);
-}
-
-/**
- * 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
- */
-static 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
- */
-static void zbud_unmap(struct zbud_pool *pool, unsigned long handle)
-{
-}
-
-/**
- * zbud_get_pool_pages() - 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.
- */
-static u64 zbud_get_pool_pages(struct zbud_pool *pool)
-{
- return pool->pages_nr;
-}
-
-/*****************
- * zpool
- ****************/
-
-static void *zbud_zpool_create(const char *name, gfp_t gfp)
-{
- return zbud_create_pool(gfp);
-}
-
-static void zbud_zpool_destroy(void *pool)
-{
- zbud_destroy_pool(pool);
-}
-
-static int zbud_zpool_malloc(void *pool, size_t size, gfp_t gfp,
- unsigned long *handle)
-{
- return zbud_alloc(pool, size, gfp, handle);
-}
-static void zbud_zpool_free(void *pool, unsigned long handle)
-{
- zbud_free(pool, handle);
-}
-
-static void *zbud_zpool_map(void *pool, unsigned long handle,
- enum zpool_mapmode mm)
-{
- return zbud_map(pool, handle);
-}
-static void zbud_zpool_unmap(void *pool, unsigned long handle)
-{
- zbud_unmap(pool, handle);
-}
-
-static u64 zbud_zpool_total_pages(void *pool)
-{
- return zbud_get_pool_pages(pool);
-}
-
-static struct zpool_driver zbud_zpool_driver = {
- .type = "zbud",
- .sleep_mapped = true,
- .owner = THIS_MODULE,
- .create = zbud_zpool_create,
- .destroy = zbud_zpool_destroy,
- .malloc = zbud_zpool_malloc,
- .free = zbud_zpool_free,
- .map = zbud_zpool_map,
- .unmap = zbud_zpool_unmap,
- .total_pages = zbud_zpool_total_pages,
-};
-
-MODULE_ALIAS("zpool-zbud");
-
-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");
-
- zpool_register_driver(&zbud_zpool_driver);
-
- return 0;
-}
-
-static void __exit exit_zbud(void)
-{
- zpool_unregister_driver(&zbud_zpool_driver);
- 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");
projects / thirdparty / linux.git / commitdiff
