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Merge branch 'akpm' (patches from Andrew Morton) 

Merge more patches from Andrew Morton:
 "The rest of MM"

* emailed patches from Andrew Morton <akpm@linux-foundation.org>:
  mm: remove free_area_cache
  zswap: add documentation
  zswap: add to mm/
  zbud: add to mm/
This commit is contained in:
Linus Torvalds 2013-07-10 18:11:43 -07:00
parent ae92494930 98d1e64f95
commit db6e330490
23 changed files with 1592 additions and 66 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

68
Documentation/vm/zswap.txt Normal file
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@ -0,0 +1,68 @@
Overview:
Zswap is a lightweight compressed cache for swap pages. It takes pages that are
in the process of being swapped out and attempts to compress them into a
dynamically allocated RAM-based memory pool. zswap basically trades CPU cycles
for potentially reduced swap I/O.  This trade-off can also result in a
significant performance improvement if reads from the compressed cache are
faster than reads from a swap device.
NOTE: Zswap is a new feature as of v3.11 and interacts heavily with memory
reclaim. This interaction has not be fully explored on the large set of
potential configurations and workloads that exist. For this reason, zswap
is a work in progress and should be considered experimental.
Some potential benefits:
* Desktop/laptop users with limited RAM capacities can mitigate the
    performance impact of swapping.
* Overcommitted guests that share a common I/O resource can
    dramatically reduce their swap I/O pressure, avoiding heavy handed I/O
throttling by the hypervisor. This allows more work to get done with less
impact to the guest workload and guests sharing the I/O subsystem
* Users with SSDs as swap devices can extend the life of the device by
    drastically reducing life-shortening writes.
Zswap evicts pages from compressed cache on an LRU basis to the backing swap
device when the compressed pool reaches it size limit. This requirement had
been identified in prior community discussions.
To enabled zswap, the "enabled" attribute must be set to 1 at boot time. e.g.
zswap.enabled=1
Design:
Zswap receives pages for compression through the Frontswap API and is able to
evict pages from its own compressed pool on an LRU basis and write them back to
the backing swap device in the case that the compressed pool is full.
Zswap makes use of zbud for the managing the compressed memory pool. Each
allocation in zbud is not directly accessible by address. Rather, a handle is
return by the allocation routine and that handle must be mapped before being
accessed. The compressed memory pool grows on demand and shrinks as compressed
pages are freed. The pool is not preallocated.
When a swap page is passed from frontswap to zswap, zswap maintains a mapping
of the swap entry, a combination of the swap type and swap offset, to the zbud
handle that references that compressed swap page. This mapping is achieved
with a red-black tree per swap type. The swap offset is the search key for the
tree nodes.
During a page fault on a PTE that is a swap entry, frontswap calls the zswap
load function to decompress the page into the page allocated by the page fault
handler.
Once there are no PTEs referencing a swap page stored in zswap (i.e. the count
in the swap_map goes to 0) the swap code calls the zswap invalidate function,
via frontswap, to free the compressed entry.
Zswap seeks to be simple in its policies. Sysfs attributes allow for one user
controlled policies:
* max_pool_percent - The maximum percentage of memory that the compressed
pool can occupy.
Zswap allows the compressor to be selected at kernel boot time by setting the
“compressor” attribute. The default compressor is lzo. e.g.
zswap.compressor=deflate
A debugfs interface is provided for various statistic about pool size, number
of pages stored, and various counters for the reasons pages are rejected.

2
arch/arm/mm/mmap.c
View File

@ -181,11 +181,9 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
if (mmap_is_legacy()) {
mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
mm->get_unmapped_area = arch_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
} else {
mm->mmap_base = mmap_base(random_factor);
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
mm->unmap_area = arch_unmap_area_topdown;
}
}

2
arch/arm64/mm/mmap.c
View File

@ -90,11 +90,9 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
if (mmap_is_legacy()) {
mm->mmap_base = TASK_UNMAPPED_BASE;
mm->get_unmapped_area = arch_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
} else {
mm->mmap_base = mmap_base();
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
mm->unmap_area = arch_unmap_area_topdown;
}
}
EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);

2
arch/mips/mm/mmap.c
View File

@ -158,11 +158,9 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
if (mmap_is_legacy()) {
mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
mm->get_unmapped_area = arch_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
} else {
mm->mmap_base = mmap_base(random_factor);
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
mm->unmap_area = arch_unmap_area_topdown;
}
}

2
arch/powerpc/mm/mmap.c
View File

@ -92,10 +92,8 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
if (mmap_is_legacy()) {
mm->mmap_base = TASK_UNMAPPED_BASE;
mm->get_unmapped_area = arch_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
} else {
mm->mmap_base = mmap_base();
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
mm->unmap_area = arch_unmap_area_topdown;
}
}

4
arch/s390/mm/mmap.c
View File

@ -91,11 +91,9 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
if (mmap_is_legacy()) {
mm->mmap_base = TASK_UNMAPPED_BASE;
mm->get_unmapped_area = arch_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
} else {
mm->mmap_base = mmap_base();
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
mm->unmap_area = arch_unmap_area_topdown;
}
}
@ -176,11 +174,9 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
if (mmap_is_legacy()) {
mm->mmap_base = TASK_UNMAPPED_BASE;
mm->get_unmapped_area = s390_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
} else {
mm->mmap_base = mmap_base();
mm->get_unmapped_area = s390_get_unmapped_area_topdown;
mm->unmap_area = arch_unmap_area_topdown;
}
}

2
arch/sparc/kernel/sys_sparc_64.c
View File

@ -290,7 +290,6 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
sysctl_legacy_va_layout) {
mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
mm->get_unmapped_area = arch_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
} else {
/* We know it's 32-bit */
unsigned long task_size = STACK_TOP32;
@ -302,7 +301,6 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
mm->mmap_base = PAGE_ALIGN(task_size - gap - random_factor);
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
mm->unmap_area = arch_unmap_area_topdown;
}
}

2
arch/tile/mm/mmap.c
View File

@ -66,10 +66,8 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
if (!is_32bit || rlimit(RLIMIT_STACK) == RLIM_INFINITY) {
mm->mmap_base = TASK_UNMAPPED_BASE;
mm->get_unmapped_area = arch_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
} else {
mm->mmap_base = mmap_base(mm);
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
mm->unmap_area = arch_unmap_area_topdown;
}
}

2
arch/x86/ia32/ia32_aout.c
View File

@ -308,8 +308,6 @@ static int load_aout_binary(struct linux_binprm *bprm)
(current->mm->start_data = N_DATADDR(ex));
current->mm->brk = ex.a_bss +
(current->mm->start_brk = N_BSSADDR(ex));
current->mm->free_area_cache = TASK_UNMAPPED_BASE;
current->mm->cached_hole_size = 0;
retval = setup_arg_pages(bprm, IA32_STACK_TOP, EXSTACK_DEFAULT);
if (retval < 0) {

2
arch/x86/mm/mmap.c
View File

@ -115,10 +115,8 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
if (mmap_is_legacy()) {
mm->mmap_base = mmap_legacy_base();
mm->get_unmapped_area = arch_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
} else {
mm->mmap_base = mmap_base();
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
mm->unmap_area = arch_unmap_area_topdown;
}
}

2
fs/binfmt_aout.c
View File

@ -255,8 +255,6 @@ static int load_aout_binary(struct linux_binprm * bprm)
(current->mm->start_data = N_DATADDR(ex));
current->mm->brk = ex.a_bss +
(current->mm->start_brk = N_BSSADDR(ex));
current->mm->free_area_cache = current->mm->mmap_base;
current->mm->cached_hole_size = 0;
retval = setup_arg_pages(bprm, STACK_TOP, EXSTACK_DEFAULT);
if (retval < 0) {

2
fs/binfmt_elf.c
View File

@ -738,8 +738,6 @@ static int load_elf_binary(struct linux_binprm *bprm)
/* Do this so that we can load the interpreter, if need be. We will
change some of these later */
current->mm->free_area_cache = current->mm->mmap_base;
current->mm->cached_hole_size = 0;
retval = setup_arg_pages(bprm, randomize_stack_top(STACK_TOP),
executable_stack);
if (retval < 0) {

3
include/linux/mm_types.h
View File

@ -330,12 +330,9 @@ struct mm_struct {
unsigned long (*get_unmapped_area) (struct file *filp,
unsigned long addr, unsigned long len,
unsigned long pgoff, unsigned long flags);
void (*unmap_area) (struct mm_struct *mm, unsigned long addr);
#endif
unsigned long mmap_base; /* base of mmap area */
unsigned long task_size; /* size of task vm space */
unsigned long cached_hole_size; /* if non-zero, the largest hole below free_area_cache */
unsigned long free_area_cache; /* first hole of size cached_hole_size or larger */
unsigned long highest_vm_end; /* highest vma end address */
pgd_t * pgd;
atomic_t mm_users; /* How many users with user space? */

2
include/linux/sched.h
View File

@ -322,8 +322,6 @@ extern unsigned long
arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
unsigned long len, unsigned long pgoff,
unsigned long flags);
extern void arch_unmap_area(struct mm_struct *, unsigned long);
extern void arch_unmap_area_topdown(struct mm_struct *, unsigned long);
#else
static inline void arch_pick_mmap_layout(struct mm_struct *mm) {}
#endif

22
include/linux/zbud.h Normal file
View File

@ -0,0 +1,22 @@
#ifndef _ZBUD_H_
#define _ZBUD_H_
#include <linux/types.h>
struct zbud_pool;
struct zbud_ops {
int (*evict)(struct zbud_pool *pool, unsigned long handle);
};
struct zbud_pool *zbud_create_pool(gfp_t gfp, struct zbud_ops *ops);
void zbud_destroy_pool(struct zbud_pool *pool);
int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp,
unsigned long *handle);
void zbud_free(struct zbud_pool *pool, unsigned long handle);
int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries);
void *zbud_map(struct zbud_pool *pool, unsigned long handle);
void zbud_unmap(struct zbud_pool *pool, unsigned long handle);
u64 zbud_get_pool_size(struct zbud_pool *pool);
#endif /* _ZBUD_H_ */

4
kernel/fork.c
View File

@ -365,8 +365,6 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
mm->locked_vm = 0;
mm->mmap = NULL;
mm->mmap_cache = NULL;
mm->free_area_cache = oldmm->mmap_base;
mm->cached_hole_size = ~0UL;
mm->map_count = 0;
cpumask_clear(mm_cpumask(mm));
mm->mm_rb = RB_ROOT;
@ -540,8 +538,6 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
mm->nr_ptes = 0;
memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
spin_lock_init(&mm->page_table_lock);
mm->free_area_cache = TASK_UNMAPPED_BASE;
mm->cached_hole_size = ~0UL;
mm_init_aio(mm);
mm_init_owner(mm, p);

30
mm/Kconfig
View File

@ -478,6 +478,36 @@ config FRONTSWAP
If unsure, say Y to enable frontswap.
config ZBUD
tristate
default n
help
A special purpose allocator for storing compressed pages.
It is designed to store up to two compressed pages per physical
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.
config ZSWAP
bool "Compressed cache for swap pages (EXPERIMENTAL)"
depends on FRONTSWAP && CRYPTO=y
select CRYPTO_LZO
select ZBUD
default n
help
A lightweight compressed cache for swap pages. It takes
pages that are in the process of being swapped out and attempts to
compress them into a dynamically allocated RAM-based memory pool.
This can result in a significant I/O reduction on swap device and,
in the case where decompressing from RAM is faster that swap device
reads, can also improve workload performance.
This is marked experimental because it is a new feature (as of
v3.11) that interacts heavily with memory reclaim. While these
interactions don't cause any known issues on simple memory setups,
they have not be fully explored on the large set of potential
configurations and workloads that exist.
config MEM_SOFT_DIRTY
bool "Track memory changes"
depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY

2
mm/Makefile
View File

@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
obj-$(CONFIG_BOUNCE) += bounce.o
obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
obj-$(CONFIG_FRONTSWAP) += frontswap.o
obj-$(CONFIG_ZSWAP) += zswap.o
obj-$(CONFIG_HAS_DMA) += dmapool.o
obj-$(CONFIG_HUGETLBFS) += hugetlb.o
obj-$(CONFIG_NUMA) += mempolicy.o
@ -58,3 +59,4 @@ obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
obj-$(CONFIG_CLEANCACHE) += cleancache.o
obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
obj-$(CONFIG_ZBUD) += zbud.o

28
mm/mmap.c
View File

@ -1878,15 +1878,6 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
}
#endif
void arch_unmap_area(struct mm_struct *mm, unsigned long addr)
{
/*
* Is this a new hole at the lowest possible address?
*/
if (addr >= TASK_UNMAPPED_BASE && addr < mm->free_area_cache)
mm->free_area_cache = addr;
}
/*
* This mmap-allocator allocates new areas top-down from below the
* stack's low limit (the base):
@ -1943,19 +1934,6 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
}
#endif
void arch_unmap_area_topdown(struct mm_struct *mm, unsigned long addr)
{
/*
* Is this a new hole at the highest possible address?
*/
if (addr > mm->free_area_cache)
mm->free_area_cache = addr;
/* dont allow allocations above current base */
if (mm->free_area_cache > mm->mmap_base)
mm->free_area_cache = mm->mmap_base;
}
unsigned long
get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
unsigned long pgoff, unsigned long flags)
@ -2376,7 +2354,6 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
{
struct vm_area_struct **insertion_point;
struct vm_area_struct *tail_vma = NULL;
unsigned long addr;
insertion_point = (prev ? &prev->vm_next : &mm->mmap);
vma->vm_prev = NULL;
@ -2393,11 +2370,6 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
} else
mm->highest_vm_end = prev ? prev->vm_end : 0;
tail_vma->vm_next = NULL;
if (mm->unmap_area == arch_unmap_area)
addr = prev ? prev->vm_end : mm->mmap_base;
else
addr = vma ? vma->vm_start : mm->mmap_base;
mm->unmap_area(mm, addr);
mm->mmap_cache = NULL; /* Kill the cache. */
}

4
mm/nommu.c
View File

@ -1871,10 +1871,6 @@ unsigned long arch_get_unmapped_area(struct file *file, unsigned long addr,
return -ENOMEM;
}
void arch_unmap_area(struct mm_struct *mm, unsigned long addr)
{
}
void unmap_mapping_range(struct address_space *mapping,
loff_t const holebegin, loff_t const holelen,
int even_cows)

1
mm/util.c
View File

@ -295,7 +295,6 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
{
mm->mmap_base = TASK_UNMAPPED_BASE;
mm->get_unmapped_area = arch_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
}
#endif

527
mm/zbud.c Normal file
View File

@ -0,0 +1,527 @@
/*
* 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
* justifed" 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/zbud.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, and there
* will be 64 freelists per pool.
*/
#define NCHUNKS_ORDER 6
#define CHUNK_SHIFT (PAGE_SHIFT - NCHUNKS_ORDER)
#define CHUNK_SIZE (1 << CHUNK_SHIFT)
#define NCHUNKS (PAGE_SIZE >> CHUNK_SHIFT)
#define ZHDR_SIZE_ALIGNED CHUNK_SIZE
/**
* 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
* @lru: list tracking the zbud pages in LRU order by most recently
* added buddy.
* @pages_nr: number of zbud pages in the pool.
* @ops: pointer to a structure of user defined operations specified at
* pool creation time.
*
* This structure is allocated at pool creation time and maintains metadata
* pertaining to a particular zbud pool.
*/
struct zbud_pool {
spinlock_t lock;
struct list_head unbuddied[NCHUNKS];
struct list_head buddied;
struct list_head lru;
u64 pages_nr;
struct zbud_ops *ops;
};
/*
* 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
* @lru: links the zbud page into the lru list 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;
struct list_head lru;
unsigned int first_chunks;
unsigned int last_chunks;
bool under_reclaim;
};
/*****************
* 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(int 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);
INIT_LIST_HEAD(&zhdr->lru);
zhdr->under_reclaim = 0;
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. -1 at the
* end for the zbud header.
*/
return NCHUNKS - zhdr->first_chunks - zhdr->last_chunks - 1;
}
/*****************
* API Functions
*****************/
/**
* zbud_create_pool() - create a new zbud pool
* @gfp: gfp flags when allocating the zbud pool structure
* @ops: user-defined operations for the zbud pool
*
* Return: pointer to the new zbud pool or NULL if the metadata allocation
* failed.
*/
struct zbud_pool *zbud_create_pool(gfp_t gfp, struct zbud_ops *ops)
{
struct zbud_pool *pool;
int i;
pool = kmalloc(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);
INIT_LIST_HEAD(&pool->lru);
pool->pages_nr = 0;
pool->ops = ops;
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.
*/
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 is the size or
* gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
* a new page.
*/
int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp,
unsigned long *handle)
{
int chunks, i, freechunks;
struct zbud_header *zhdr = NULL;
enum buddy bud;
struct page *page;
if (size <= 0 || gfp & __GFP_HIGHMEM)
return -EINVAL;
if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED)
return -ENOSPC;
chunks = size_to_chunks(size);
spin_lock(&pool->lock);
/* First, try to find an unbuddied zbud page. */
zhdr = NULL;
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);
}
/* Add/move zbud page to beginning of LRU */
if (!list_empty(&zhdr->lru))
list_del(&zhdr->lru);
list_add(&zhdr->lru, &pool->lru);
*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()
*
* In the case that the zbud page in which the allocation resides is under
* reclaim, as indicated by the PG_reclaim flag being set, this function
* only sets the first|last_chunks to 0. The page is actually freed
* once both buddies are evicted (see zbud_reclaim_page() below).
*/
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;
if (zhdr->under_reclaim) {
/* zbud page is under reclaim, reclaim will free */
spin_unlock(&pool->lock);
return;
}
/* Remove from existing buddy list */
list_del(&zhdr->buddy);
if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
/* zbud page is empty, free */
list_del(&zhdr->lru);
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);
}
#define list_tail_entry(ptr, type, member) \
list_entry((ptr)->prev, type, member)
/**
* zbud_reclaim_page() - evicts allocations from a pool page and frees it
* @pool: pool from which a page will attempt to be evicted
* @retires: number of pages on the LRU list for which eviction will
* be attempted before failing
*
* zbud reclaim is different from normal system reclaim in that the reclaim is
* done from the bottom, up. This is because only the bottom layer, zbud, has
* information on how the allocations are organized within each zbud page. This
* has the potential to create interesting locking situations between zbud and
* the user, however.
*
* To avoid these, this is how zbud_reclaim_page() should be called:
* The user detects a page should be reclaimed and calls zbud_reclaim_page().
* zbud_reclaim_page() will remove a zbud page from the pool LRU list and call
* the user-defined eviction handler with the pool and handle as arguments.
*
* If the handle can not be evicted, the eviction handler should return
* non-zero. zbud_reclaim_page() will add the zbud page back to the
* appropriate list and try the next zbud page on the LRU up to
* a user defined number of retries.
*
* If the handle is successfully evicted, the eviction handler should
* 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_tail_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");
return 0;
}
static void __exit exit_zbud(void)
{
pr_info("unloaded\n");
}
module_init(init_zbud);
module_exit(exit_zbud);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
MODULE_DESCRIPTION("Buddy Allocator for Compressed Pages");

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mm/zswap.c Normal file
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@ -0,0 +1,943 @@
/*
* zswap.c - zswap driver file
*
* zswap is a backend for frontswap that takes pages that are in the process
* of being swapped out and attempts to compress and store them in a
* RAM-based memory pool. This can result in a significant I/O reduction on
* the swap device and, in the case where decompressing from RAM is faster
* than reading from the swap device, can also improve workload performance.
*
* Copyright (C) 2012 Seth Jennings <sjenning@linux.vnet.ibm.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/cpu.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/atomic.h>
#include <linux/frontswap.h>
#include <linux/rbtree.h>
#include <linux/swap.h>
#include <linux/crypto.h>
#include <linux/mempool.h>
#include <linux/zbud.h>
#include <linux/mm_types.h>
#include <linux/page-flags.h>
#include <linux/swapops.h>
#include <linux/writeback.h>
#include <linux/pagemap.h>
/*********************************
* statistics
**********************************/
/* Number of memory pages used by the compressed pool */
static u64 zswap_pool_pages;
/* The number of compressed pages currently stored in zswap */
static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
/*
* The statistics below are not protected from concurrent access for
* performance reasons so they may not be a 100% accurate. However,
* they do provide useful information on roughly how many times a
* certain event is occurring.
*/
/* Pool limit was hit (see zswap_max_pool_percent) */
static u64 zswap_pool_limit_hit;
/* Pages written back when pool limit was reached */
static u64 zswap_written_back_pages;
/* Store failed due to a reclaim failure after pool limit was reached */
static u64 zswap_reject_reclaim_fail;
/* Compressed page was too big for the allocator to (optimally) store */
static u64 zswap_reject_compress_poor;
/* Store failed because underlying allocator could not get memory */
static u64 zswap_reject_alloc_fail;
/* Store failed because the entry metadata could not be allocated (rare) */
static u64 zswap_reject_kmemcache_fail;
/* Duplicate store was encountered (rare) */
static u64 zswap_duplicate_entry;
/*********************************
* tunables
**********************************/
/* Enable/disable zswap (disabled by default, fixed at boot for now) */
static bool zswap_enabled __read_mostly;
module_param_named(enabled, zswap_enabled, bool, 0);
/* Compressor to be used by zswap (fixed at boot for now) */
#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
module_param_named(compressor, zswap_compressor, charp, 0);
/* The maximum percentage of memory that the compressed pool can occupy */
static unsigned int zswap_max_pool_percent = 20;
module_param_named(max_pool_percent,
zswap_max_pool_percent, uint, 0644);
/*********************************
* compression functions
**********************************/
/* per-cpu compression transforms */
static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
enum comp_op {
ZSWAP_COMPOP_COMPRESS,
ZSWAP_COMPOP_DECOMPRESS
};
static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
u8 *dst, unsigned int *dlen)
{
struct crypto_comp *tfm;
int ret;
tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
switch (op) {
case ZSWAP_COMPOP_COMPRESS:
ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
break;
case ZSWAP_COMPOP_DECOMPRESS:
ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
break;
default:
ret = -EINVAL;
}
put_cpu();
return ret;
}
static int __init zswap_comp_init(void)
{
if (!crypto_has_comp(zswap_compressor, 0, 0)) {
pr_info("%s compressor not available\n", zswap_compressor);
/* fall back to default compressor */
zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
if (!crypto_has_comp(zswap_compressor, 0, 0))
/* can't even load the default compressor */
return -ENODEV;
}
pr_info("using %s compressor\n", zswap_compressor);
/* alloc percpu transforms */
zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
if (!zswap_comp_pcpu_tfms)
return -ENOMEM;
return 0;
}
static void zswap_comp_exit(void)
{
/* free percpu transforms */
if (zswap_comp_pcpu_tfms)
free_percpu(zswap_comp_pcpu_tfms);
}
/*********************************
* data structures
**********************************/
/*
* struct zswap_entry
*
* This structure contains the metadata for tracking a single compressed
* page within zswap.
*
* rbnode - links the entry into red-black tree for the appropriate swap type
* refcount - the number of outstanding reference to the entry. This is needed
* to protect against premature freeing of the entry by code
* concurent calls to load, invalidate, and writeback. The lock
* for the zswap_tree structure that contains the entry must
* be held while changing the refcount. Since the lock must
* be held, there is no reason to also make refcount atomic.
* offset - the swap offset for the entry. Index into the red-black tree.
* handle - zsmalloc allocation handle that stores the compressed page data
* length - the length in bytes of the compressed page data. Needed during
* decompression
*/
struct zswap_entry {
struct rb_node rbnode;
pgoff_t offset;
int refcount;
unsigned int length;
unsigned long handle;
};
struct zswap_header {
swp_entry_t swpentry;
};
/*
* The tree lock in the zswap_tree struct protects a few things:
* - the rbtree
* - the refcount field of each entry in the tree
*/
struct zswap_tree {
struct rb_root rbroot;
spinlock_t lock;
struct zbud_pool *pool;
};
static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
/*********************************
* zswap entry functions
**********************************/
static struct kmem_cache *zswap_entry_cache;
static int zswap_entry_cache_create(void)
{
zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
return (zswap_entry_cache == NULL);
}
static void zswap_entry_cache_destory(void)
{
kmem_cache_destroy(zswap_entry_cache);
}
static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
{
struct zswap_entry *entry;
entry = kmem_cache_alloc(zswap_entry_cache, gfp);
if (!entry)
return NULL;
entry->refcount = 1;
return entry;
}
static void zswap_entry_cache_free(struct zswap_entry *entry)
{
kmem_cache_free(zswap_entry_cache, entry);
}
/* caller must hold the tree lock */
static void zswap_entry_get(struct zswap_entry *entry)
{
entry->refcount++;
}
/* caller must hold the tree lock */
static int zswap_entry_put(struct zswap_entry *entry)
{
entry->refcount--;
return entry->refcount;
}
/*********************************
* rbtree functions
**********************************/
static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
{
struct rb_node *node = root->rb_node;
struct zswap_entry *entry;
while (node) {
entry = rb_entry(node, struct zswap_entry, rbnode);
if (entry->offset > offset)
node = node->rb_left;
else if (entry->offset < offset)
node = node->rb_right;
else
return entry;
}
return NULL;
}
/*
* In the case that a entry with the same offset is found, a pointer to
* the existing entry is stored in dupentry and the function returns -EEXIST
*/
static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
struct zswap_entry **dupentry)
{
struct rb_node **link = &root->rb_node, *parent = NULL;
struct zswap_entry *myentry;
while (*link) {
parent = *link;
myentry = rb_entry(parent, struct zswap_entry, rbnode);
if (myentry->offset > entry->offset)
link = &(*link)->rb_left;
else if (myentry->offset < entry->offset)
link = &(*link)->rb_right;
else {
*dupentry = myentry;
return -EEXIST;
}
}
rb_link_node(&entry->rbnode, parent, link);
rb_insert_color(&entry->rbnode, root);
return 0;
}
/*********************************
* per-cpu code
**********************************/
static DEFINE_PER_CPU(u8 *, zswap_dstmem);
static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
{
struct crypto_comp *tfm;
u8 *dst;
switch (action) {
case CPU_UP_PREPARE:
tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
if (IS_ERR(tfm)) {
pr_err("can't allocate compressor transform\n");
return NOTIFY_BAD;
}
*per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
dst = kmalloc(PAGE_SIZE * 2, GFP_KERNEL);
if (!dst) {
pr_err("can't allocate compressor buffer\n");
crypto_free_comp(tfm);
*per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
return NOTIFY_BAD;
}
per_cpu(zswap_dstmem, cpu) = dst;
break;
case CPU_DEAD:
case CPU_UP_CANCELED:
tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
if (tfm) {
crypto_free_comp(tfm);
*per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
}
dst = per_cpu(zswap_dstmem, cpu);
kfree(dst);
per_cpu(zswap_dstmem, cpu) = NULL;
break;
default:
break;
}
return NOTIFY_OK;
}
static int zswap_cpu_notifier(struct notifier_block *nb,
unsigned long action, void *pcpu)
{
unsigned long cpu = (unsigned long)pcpu;
return __zswap_cpu_notifier(action, cpu);
}
static struct notifier_block zswap_cpu_notifier_block = {
.notifier_call = zswap_cpu_notifier
};
static int zswap_cpu_init(void)
{
unsigned long cpu;
get_online_cpus();
for_each_online_cpu(cpu)
if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
goto cleanup;
register_cpu_notifier(&zswap_cpu_notifier_block);
put_online_cpus();
return 0;
cleanup:
for_each_online_cpu(cpu)
__zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
put_online_cpus();
return -ENOMEM;
}
/*********************************
* helpers
**********************************/
static bool zswap_is_full(void)
{
return (totalram_pages * zswap_max_pool_percent / 100 <
zswap_pool_pages);
}
/*
* Carries out the common pattern of freeing and entry's zsmalloc allocation,
* freeing the entry itself, and decrementing the number of stored pages.
*/
static void zswap_free_entry(struct zswap_tree *tree, struct zswap_entry *entry)
{
zbud_free(tree->pool, entry->handle);
zswap_entry_cache_free(entry);
atomic_dec(&zswap_stored_pages);
zswap_pool_pages = zbud_get_pool_size(tree->pool);
}
/*********************************
* writeback code
**********************************/
/* return enum for zswap_get_swap_cache_page */
enum zswap_get_swap_ret {
ZSWAP_SWAPCACHE_NEW,
ZSWAP_SWAPCACHE_EXIST,
ZSWAP_SWAPCACHE_NOMEM
};
/*
* zswap_get_swap_cache_page
*
* This is an adaption of read_swap_cache_async()
*
* This function tries to find a page with the given swap entry
* in the swapper_space address space (the swap cache). If the page
* is found, it is returned in retpage. Otherwise, a page is allocated,
* added to the swap cache, and returned in retpage.
*
* If success, the swap cache page is returned in retpage
* Returns 0 if page was already in the swap cache, page is not locked
* Returns 1 if the new page needs to be populated, page is locked
* Returns <0 on error
*/
static int zswap_get_swap_cache_page(swp_entry_t entry,
struct page **retpage)
{
struct page *found_page, *new_page = NULL;
struct address_space *swapper_space = &swapper_spaces[swp_type(entry)];
int err;
*retpage = NULL;
do {
/*
* First check the swap cache. Since this is normally
* called after lookup_swap_cache() failed, re-calling
* that would confuse statistics.
*/
found_page = find_get_page(swapper_space, entry.val);
if (found_page)
break;
/*
* Get a new page to read into from swap.
*/
if (!new_page) {
new_page = alloc_page(GFP_KERNEL);
if (!new_page)
break; /* Out of memory */
}
/*
* call radix_tree_preload() while we can wait.
*/
err = radix_tree_preload(GFP_KERNEL);
if (err)
break;
/*
* Swap entry may have been freed since our caller observed it.
*/
err = swapcache_prepare(entry);
if (err == -EEXIST) { /* seems racy */
radix_tree_preload_end();
continue;
}
if (err) { /* swp entry is obsolete ? */
radix_tree_preload_end();
break;
}
/* May fail (-ENOMEM) if radix-tree node allocation failed. */
__set_page_locked(new_page);
SetPageSwapBacked(new_page);
err = __add_to_swap_cache(new_page, entry);
if (likely(!err)) {
radix_tree_preload_end();
lru_cache_add_anon(new_page);
*retpage = new_page;
return ZSWAP_SWAPCACHE_NEW;
}
radix_tree_preload_end();
ClearPageSwapBacked(new_page);
__clear_page_locked(new_page);
/*
* add_to_swap_cache() doesn't return -EEXIST, so we can safely
* clear SWAP_HAS_CACHE flag.
*/
swapcache_free(entry, NULL);
} while (err != -ENOMEM);
if (new_page)
page_cache_release(new_page);
if (!found_page)
return ZSWAP_SWAPCACHE_NOMEM;
*retpage = found_page;
return ZSWAP_SWAPCACHE_EXIST;
}
/*
* Attempts to free an entry by adding a page to the swap cache,
* decompressing the entry data into the page, and issuing a
* bio write to write the page back to the swap device.
*
* This can be thought of as a "resumed writeback" of the page
* to the swap device. We are basically resuming the same swap
* writeback path that was intercepted with the frontswap_store()
* in the first place. After the page has been decompressed into
* the swap cache, the compressed version stored by zswap can be
* freed.
*/
static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle)
{
struct zswap_header *zhdr;
swp_entry_t swpentry;
struct zswap_tree *tree;
pgoff_t offset;
struct zswap_entry *entry;
struct page *page;
u8 *src, *dst;
unsigned int dlen;
int ret, refcount;
struct writeback_control wbc = {
.sync_mode = WB_SYNC_NONE,
};
/* extract swpentry from data */
zhdr = zbud_map(pool, handle);
swpentry = zhdr->swpentry; /* here */
zbud_unmap(pool, handle);
tree = zswap_trees[swp_type(swpentry)];
offset = swp_offset(swpentry);
BUG_ON(pool != tree->pool);
/* find and ref zswap entry */
spin_lock(&tree->lock);
entry = zswap_rb_search(&tree->rbroot, offset);
if (!entry) {
/* entry was invalidated */
spin_unlock(&tree->lock);
return 0;
}
zswap_entry_get(entry);
spin_unlock(&tree->lock);
BUG_ON(offset != entry->offset);
/* try to allocate swap cache page */
switch (zswap_get_swap_cache_page(swpentry, &page)) {
case ZSWAP_SWAPCACHE_NOMEM: /* no memory */
ret = -ENOMEM;
goto fail;
case ZSWAP_SWAPCACHE_EXIST: /* page is unlocked */
/* page is already in the swap cache, ignore for now */
page_cache_release(page);
ret = -EEXIST;
goto fail;
case ZSWAP_SWAPCACHE_NEW: /* page is locked */
/* decompress */
dlen = PAGE_SIZE;
src = (u8 *)zbud_map(tree->pool, entry->handle) +
sizeof(struct zswap_header);
dst = kmap_atomic(page);
ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src,
entry->length, dst, &dlen);
kunmap_atomic(dst);
zbud_unmap(tree->pool, entry->handle);
BUG_ON(ret);
BUG_ON(dlen != PAGE_SIZE);
/* page is up to date */
SetPageUptodate(page);
}
/* start writeback */
__swap_writepage(page, &wbc, end_swap_bio_write);
page_cache_release(page);
zswap_written_back_pages++;
spin_lock(&tree->lock);
/* drop local reference */
zswap_entry_put(entry);
/* drop the initial reference from entry creation */
refcount = zswap_entry_put(entry);
/*
* There are three possible values for refcount here:
* (1) refcount is 1, load is in progress, unlink from rbtree,
* load will free
* (2) refcount is 0, (normal case) entry is valid,
* remove from rbtree and free entry
* (3) refcount is -1, invalidate happened during writeback,
* free entry
*/
if (refcount >= 0) {
/* no invalidate yet, remove from rbtree */
rb_erase(&entry->rbnode, &tree->rbroot);
}
spin_unlock(&tree->lock);
if (refcount <= 0) {
/* free the entry */
zswap_free_entry(tree, entry);
return 0;
}
return -EAGAIN;
fail:
spin_lock(&tree->lock);
zswap_entry_put(entry);
spin_unlock(&tree->lock);
return ret;
}
/*********************************
* frontswap hooks
**********************************/
/* attempts to compress and store an single page */
static int zswap_frontswap_store(unsigned type, pgoff_t offset,
struct page *page)
{
struct zswap_tree *tree = zswap_trees[type];
struct zswap_entry *entry, *dupentry;
int ret;
unsigned int dlen = PAGE_SIZE, len;
unsigned long handle;
char *buf;
u8 *src, *dst;
struct zswap_header *zhdr;
if (!tree) {
ret = -ENODEV;
goto reject;
}
/* reclaim space if needed */
if (zswap_is_full()) {
zswap_pool_limit_hit++;
if (zbud_reclaim_page(tree->pool, 8)) {
zswap_reject_reclaim_fail++;
ret = -ENOMEM;
goto reject;
}
}
/* allocate entry */
entry = zswap_entry_cache_alloc(GFP_KERNEL);
if (!entry) {
zswap_reject_kmemcache_fail++;
ret = -ENOMEM;
goto reject;
}
/* compress */
dst = get_cpu_var(zswap_dstmem);
src = kmap_atomic(page);
ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
kunmap_atomic(src);
if (ret) {
ret = -EINVAL;
goto freepage;
}
/* store */
len = dlen + sizeof(struct zswap_header);
ret = zbud_alloc(tree->pool, len, __GFP_NORETRY | __GFP_NOWARN,
&handle);
if (ret == -ENOSPC) {
zswap_reject_compress_poor++;
goto freepage;
}
if (ret) {
zswap_reject_alloc_fail++;
goto freepage;
}
zhdr = zbud_map(tree->pool, handle);
zhdr->swpentry = swp_entry(type, offset);
buf = (u8 *)(zhdr + 1);
memcpy(buf, dst, dlen);
zbud_unmap(tree->pool, handle);
put_cpu_var(zswap_dstmem);
/* populate entry */
entry->offset = offset;
entry->handle = handle;
entry->length = dlen;
/* map */
spin_lock(&tree->lock);
do {
ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
if (ret == -EEXIST) {
zswap_duplicate_entry++;
/* remove from rbtree */
rb_erase(&dupentry->rbnode, &tree->rbroot);
if (!zswap_entry_put(dupentry)) {
/* free */
zswap_free_entry(tree, dupentry);
}
}
} while (ret == -EEXIST);
spin_unlock(&tree->lock);
/* update stats */
atomic_inc(&zswap_stored_pages);
zswap_pool_pages = zbud_get_pool_size(tree->pool);
return 0;
freepage:
put_cpu_var(zswap_dstmem);
zswap_entry_cache_free(entry);
reject:
return ret;
}
/*
* returns 0 if the page was successfully decompressed
* return -1 on entry not found or error
*/
static int zswap_frontswap_load(unsigned type, pgoff_t offset,
struct page *page)
{
struct zswap_tree *tree = zswap_trees[type];
struct zswap_entry *entry;
u8 *src, *dst;
unsigned int dlen;
int refcount, ret;
/* find */
spin_lock(&tree->lock);
entry = zswap_rb_search(&tree->rbroot, offset);
if (!entry) {
/* entry was written back */
spin_unlock(&tree->lock);
return -1;
}
zswap_entry_get(entry);
spin_unlock(&tree->lock);
/* decompress */
dlen = PAGE_SIZE;
src = (u8 *)zbud_map(tree->pool, entry->handle) +
sizeof(struct zswap_header);
dst = kmap_atomic(page);
ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
dst, &dlen);
kunmap_atomic(dst);
zbud_unmap(tree->pool, entry->handle);
BUG_ON(ret);
spin_lock(&tree->lock);
refcount = zswap_entry_put(entry);
if (likely(refcount)) {
spin_unlock(&tree->lock);
return 0;
}
spin_unlock(&tree->lock);
/*
* We don't have to unlink from the rbtree because
* zswap_writeback_entry() or zswap_frontswap_invalidate page()
* has already done this for us if we are the last reference.
*/
/* free */
zswap_free_entry(tree, entry);
return 0;
}
/* frees an entry in zswap */
static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
{
struct zswap_tree *tree = zswap_trees[type];
struct zswap_entry *entry;
int refcount;
/* find */
spin_lock(&tree->lock);
entry = zswap_rb_search(&tree->rbroot, offset);
if (!entry) {
/* entry was written back */
spin_unlock(&tree->lock);
return;
}
/* remove from rbtree */
rb_erase(&entry->rbnode, &tree->rbroot);
/* drop the initial reference from entry creation */
refcount = zswap_entry_put(entry);
spin_unlock(&tree->lock);
if (refcount) {
/* writeback in progress, writeback will free */
return;
}
/* free */
zswap_free_entry(tree, entry);
}
/* frees all zswap entries for the given swap type */
static void zswap_frontswap_invalidate_area(unsigned type)
{
struct zswap_tree *tree = zswap_trees[type];
struct rb_node *node;
struct zswap_entry *entry;
if (!tree)
return;
/* walk the tree and free everything */
spin_lock(&tree->lock);
/*
* TODO: Even though this code should not be executed because
* the try_to_unuse() in swapoff should have emptied the tree,
* it is very wasteful to rebalance the tree after every
* removal when we are freeing the whole tree.
*
* If post-order traversal code is ever added to the rbtree
* implementation, it should be used here.
*/
while ((node = rb_first(&tree->rbroot))) {
entry = rb_entry(node, struct zswap_entry, rbnode);
rb_erase(&entry->rbnode, &tree->rbroot);
zbud_free(tree->pool, entry->handle);
zswap_entry_cache_free(entry);
atomic_dec(&zswap_stored_pages);
}
tree->rbroot = RB_ROOT;
spin_unlock(&tree->lock);
}
static struct zbud_ops zswap_zbud_ops = {
.evict = zswap_writeback_entry
};
static void zswap_frontswap_init(unsigned type)
{
struct zswap_tree *tree;
tree = kzalloc(sizeof(struct zswap_tree), GFP_KERNEL);
if (!tree)
goto err;
tree->pool = zbud_create_pool(GFP_KERNEL, &zswap_zbud_ops);
if (!tree->pool)
goto freetree;
tree->rbroot = RB_ROOT;
spin_lock_init(&tree->lock);
zswap_trees[type] = tree;
return;
freetree:
kfree(tree);
err:
pr_err("alloc failed, zswap disabled for swap type %d\n", type);
}
static struct frontswap_ops zswap_frontswap_ops = {
.store = zswap_frontswap_store,
.load = zswap_frontswap_load,
.invalidate_page = zswap_frontswap_invalidate_page,
.invalidate_area = zswap_frontswap_invalidate_area,
.init = zswap_frontswap_init
};
/*********************************
* debugfs functions
**********************************/
#ifdef CONFIG_DEBUG_FS
#include <linux/debugfs.h>
static struct dentry *zswap_debugfs_root;
static int __init zswap_debugfs_init(void)
{
if (!debugfs_initialized())
return -ENODEV;
zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
if (!zswap_debugfs_root)
return -ENOMEM;
debugfs_create_u64("pool_limit_hit", S_IRUGO,
zswap_debugfs_root, &zswap_pool_limit_hit);
debugfs_create_u64("reject_reclaim_fail", S_IRUGO,
zswap_debugfs_root, &zswap_reject_reclaim_fail);
debugfs_create_u64("reject_alloc_fail", S_IRUGO,
zswap_debugfs_root, &zswap_reject_alloc_fail);
debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
zswap_debugfs_root, &zswap_reject_kmemcache_fail);
debugfs_create_u64("reject_compress_poor", S_IRUGO,
zswap_debugfs_root, &zswap_reject_compress_poor);
debugfs_create_u64("written_back_pages", S_IRUGO,
zswap_debugfs_root, &zswap_written_back_pages);
debugfs_create_u64("duplicate_entry", S_IRUGO,
zswap_debugfs_root, &zswap_duplicate_entry);
debugfs_create_u64("pool_pages", S_IRUGO,
zswap_debugfs_root, &zswap_pool_pages);
debugfs_create_atomic_t("stored_pages", S_IRUGO,
zswap_debugfs_root, &zswap_stored_pages);
return 0;
}
static void __exit zswap_debugfs_exit(void)
{
debugfs_remove_recursive(zswap_debugfs_root);
}
#else
static int __init zswap_debugfs_init(void)
{
return 0;
}
static void __exit zswap_debugfs_exit(void) { }
#endif
/*********************************
* module init and exit
**********************************/
static int __init init_zswap(void)
{
if (!zswap_enabled)
return 0;
pr_info("loading zswap\n");
if (zswap_entry_cache_create()) {
pr_err("entry cache creation failed\n");
goto error;
}
if (zswap_comp_init()) {
pr_err("compressor initialization failed\n");
goto compfail;
}
if (zswap_cpu_init()) {
pr_err("per-cpu initialization failed\n");
goto pcpufail;
}
frontswap_register_ops(&zswap_frontswap_ops);
if (zswap_debugfs_init())
pr_warn("debugfs initialization failed\n");
return 0;
pcpufail:
zswap_comp_exit();
compfail:
zswap_entry_cache_destory();
error:
return -ENOMEM;
}
/* must be late so crypto has time to come up */
late_initcall(init_zswap);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
MODULE_DESCRIPTION("Compressed cache for swap pages");