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mm: modify swap_map and add SWAP_HAS_CACHE flag

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This is a part of the patches for fixing memcg's swap accountinf leak.
But, IMHO, not a bad patch even if no memcg.

There are 2 kinds of references to swap.
 - reference from swap entry
 - reference from swap cache

Then,

 - If there is swap cache && swap's refcnt is 1, there is only swap cache.
  (*) swapcount(entry) == 1 && find_get_page(swapper_space, entry) != NULL

This counting logic have worked well for a long time.  But considering
that we cannot know there is a _real_ reference or not by swap_map[],
current usage of counter is not very good.

This patch adds a flag SWAP_HAS_CACHE and recored information that a swap
entry has a cache or not.  This will remove -1 magic used in swapfile.c
and be a help to avoid unnecessary find_get_page().

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KAMEZAWA Hiroyuki 2009-06-16 15:32:53 -07:00 • committed by Linus Torvalds
parent cb4b86ba47
commit 355cfa73dd
3 changed files with 171 additions and 60 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

14
include/linux/swap.h
View file

@ -129,9 +129,10 @@ enum {
#define SWAP_CLUSTER_MAX 32
#define SWAP_MAP_MAX 0x7fff
#define SWAP_MAP_BAD 0x8000
#define SWAP_MAP_MAX 0x7ffe
#define SWAP_MAP_BAD 0x7fff
#define SWAP_HAS_CACHE 0x8000 /* There is a swap cache of entry. */
#define SWAP_COUNT_MASK (~SWAP_HAS_CACHE)
/*
* The in-memory structure used to track swap areas.
*/
@ -281,7 +282,7 @@ extern long total_swap_pages;
extern void si_swapinfo(struct sysinfo *);
extern swp_entry_t get_swap_page(void);
extern swp_entry_t get_swap_page_of_type(int);
extern int swap_duplicate(swp_entry_t);
extern void swap_duplicate(swp_entry_t);
extern int swapcache_prepare(swp_entry_t);
extern int valid_swaphandles(swp_entry_t, unsigned long *);
extern void swap_free(swp_entry_t);
@ -353,9 +354,12 @@ static inline void show_swap_cache_info(void)
}
#define free_swap_and_cache(swp) is_migration_entry(swp)
#define swap_duplicate(swp) is_migration_entry(swp)
#define swapcache_prepare(swp) is_migration_entry(swp)
static inline void swap_duplicate(swp_entry_t swp)
{
}
static inline void swap_free(swp_entry_t swp)
{
}

5
mm/swap_state.c
View file

@ -292,7 +292,10 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
/*
* Swap entry may have been freed since our caller observed it.
*/
if (!swapcache_prepare(entry))
err = swapcache_prepare(entry);
if (err == -EEXIST) /* seems racy */
continue;
if (err) /* swp entry is obsolete ? */
break;
/*

212
mm/swapfile.c
View file

@ -53,6 +53,33 @@ static struct swap_info_struct swap_info[MAX_SWAPFILES];
static DEFINE_MUTEX(swapon_mutex);
/* For reference count accounting in swap_map */
/* enum for swap_map[] handling. internal use only */
enum {
SWAP_MAP = 0, /* ops for reference from swap users */
SWAP_CACHE, /* ops for reference from swap cache */
};
static inline int swap_count(unsigned short ent)
{
return ent & SWAP_COUNT_MASK;
}
static inline bool swap_has_cache(unsigned short ent)
{
return !!(ent & SWAP_HAS_CACHE);
}
static inline unsigned short encode_swapmap(int count, bool has_cache)
{
unsigned short ret = count;
if (has_cache)
return SWAP_HAS_CACHE | ret;
return ret;
}
/*
* We need this because the bdev->unplug_fn can sleep and we cannot
* hold swap_lock while calling the unplug_fn. And swap_lock
@ -167,7 +194,8 @@ static int wait_for_discard(void *word)
#define SWAPFILE_CLUSTER 256
#define LATENCY_LIMIT 256
static inline unsigned long scan_swap_map(struct swap_info_struct *si)
static inline unsigned long scan_swap_map(struct swap_info_struct *si,
int cache)
{
unsigned long offset;
unsigned long scan_base;
@ -285,7 +313,10 @@ checks:
si->lowest_bit = si->max;
si->highest_bit = 0;
}
si->swap_map[offset] = 1;
if (cache == SWAP_CACHE) /* at usual swap-out via vmscan.c */
si->swap_map[offset] = encode_swapmap(0, true);
else /* at suspend */
si->swap_map[offset] = encode_swapmap(1, false);
si->cluster_next = offset + 1;
si->flags -= SWP_SCANNING;
@ -401,7 +432,8 @@ swp_entry_t get_swap_page(void)
continue;
swap_list.next = next;
offset = scan_swap_map(si);
/* This is called for allocating swap entry for cache */
offset = scan_swap_map(si, SWAP_CACHE);
if (offset) {
spin_unlock(&swap_lock);
return swp_entry(type, offset);
@ -415,6 +447,7 @@ noswap:
return (swp_entry_t) {0};
}
/* The only caller of this function is now susupend routine */
swp_entry_t get_swap_page_of_type(int type)
{
struct swap_info_struct *si;
@ -424,7 +457,8 @@ swp_entry_t get_swap_page_of_type(int type)
si = swap_info + type;
if (si->flags & SWP_WRITEOK) {
nr_swap_pages--;
offset = scan_swap_map(si);
/* This is called for allocating swap entry, not cache */
offset = scan_swap_map(si, SWAP_MAP);
if (offset) {
spin_unlock(&swap_lock);
return swp_entry(type, offset);
@ -471,25 +505,38 @@ out:
return NULL;
}
static int swap_entry_free(struct swap_info_struct *p, swp_entry_t ent)
static int swap_entry_free(struct swap_info_struct *p,
swp_entry_t ent, int cache)
{
unsigned long offset = swp_offset(ent);
int count = p->swap_map[offset];
int count = swap_count(p->swap_map[offset]);
bool has_cache;
if (count < SWAP_MAP_MAX) {
count--;
p->swap_map[offset] = count;
if (!count) {
if (offset < p->lowest_bit)
p->lowest_bit = offset;
if (offset > p->highest_bit)
p->highest_bit = offset;
if (p->prio > swap_info[swap_list.next].prio)
swap_list.next = p - swap_info;
nr_swap_pages++;
p->inuse_pages--;
mem_cgroup_uncharge_swap(ent);
has_cache = swap_has_cache(p->swap_map[offset]);
if (cache == SWAP_MAP) { /* dropping usage count of swap */
if (count < SWAP_MAP_MAX) {
count--;
p->swap_map[offset] = encode_swapmap(count, has_cache);
}
} else { /* dropping swap cache flag */
VM_BUG_ON(!has_cache);
p->swap_map[offset] = encode_swapmap(count, false);
}
/* return code. */
count = p->swap_map[offset];
/* free if no reference */
if (!count) {
if (offset < p->lowest_bit)
p->lowest_bit = offset;
if (offset > p->highest_bit)
p->highest_bit = offset;
if (p->prio > swap_info[swap_list.next].prio)
swap_list.next = p - swap_info;
nr_swap_pages++;
p->inuse_pages--;
mem_cgroup_uncharge_swap(ent);
}
return count;
}
@ -504,7 +551,7 @@ void swap_free(swp_entry_t entry)
p = swap_info_get(entry);
if (p) {
swap_entry_free(p, entry);
swap_entry_free(p, entry, SWAP_MAP);
spin_unlock(&swap_lock);
}
}
@ -514,9 +561,16 @@ void swap_free(swp_entry_t entry)
*/
void swapcache_free(swp_entry_t entry, struct page *page)
{
struct swap_info_struct *p;
if (page)
mem_cgroup_uncharge_swapcache(page, entry);
return swap_free(entry);
p = swap_info_get(entry);
if (p) {
swap_entry_free(p, entry, SWAP_CACHE);
spin_unlock(&swap_lock);
}
return;
}
/*
@ -531,8 +585,7 @@ static inline int page_swapcount(struct page *page)
entry.val = page_private(page);
p = swap_info_get(entry);
if (p) {
/* Subtract the 1 for the swap cache itself */
count = p->swap_map[swp_offset(entry)] - 1;
count = swap_count(p->swap_map[swp_offset(entry)]);
spin_unlock(&swap_lock);
}
return count;
@ -594,7 +647,7 @@ int free_swap_and_cache(swp_entry_t entry)
p = swap_info_get(entry);
if (p) {
if (swap_entry_free(p, entry) == 1) {
if (swap_entry_free(p, entry, SWAP_MAP) == SWAP_HAS_CACHE) {
page = find_get_page(&swapper_space, entry.val);
if (page && !trylock_page(page)) {
page_cache_release(page);
@ -901,7 +954,7 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
i = 1;
}
count = si->swap_map[i];
if (count && count != SWAP_MAP_BAD)
if (count && swap_count(count) != SWAP_MAP_BAD)
break;
}
return i;
@ -1005,13 +1058,13 @@ static int try_to_unuse(unsigned int type)
*/
shmem = 0;
swcount = *swap_map;
if (swcount > 1) {
if (swap_count(swcount)) {
if (start_mm == &init_mm)
shmem = shmem_unuse(entry, page);
else
retval = unuse_mm(start_mm, entry, page);
}
if (*swap_map > 1) {
if (swap_count(*swap_map)) {
int set_start_mm = (*swap_map >= swcount);
struct list_head *p = &start_mm->mmlist;
struct mm_struct *new_start_mm = start_mm;
@ -1021,7 +1074,7 @@ static int try_to_unuse(unsigned int type)
atomic_inc(&new_start_mm->mm_users);
atomic_inc(&prev_mm->mm_users);
spin_lock(&mmlist_lock);
while (*swap_map > 1 && !retval && !shmem &&
while (swap_count(*swap_map) && !retval && !shmem &&
(p = p->next) != &start_mm->mmlist) {
mm = list_entry(p, struct mm_struct, mmlist);
if (!atomic_inc_not_zero(&mm->mm_users))
@ -1033,14 +1086,16 @@ static int try_to_unuse(unsigned int type)
cond_resched();
swcount = *swap_map;
if (swcount <= 1)
if (!swap_count(swcount)) /* any usage ? */
;
else if (mm == &init_mm) {
set_start_mm = 1;
shmem = shmem_unuse(entry, page);
} else
retval = unuse_mm(mm, entry, page);
if (set_start_mm && *swap_map < swcount) {
if (set_start_mm &&
swap_count(*swap_map) < swcount) {
mmput(new_start_mm);
atomic_inc(&mm->mm_users);
new_start_mm = mm;
@ -1067,21 +1122,25 @@ static int try_to_unuse(unsigned int type)
}
/*
* How could swap count reach 0x7fff when the maximum
* pid is 0x7fff, and there's no way to repeat a swap
* page within an mm (except in shmem, where it's the
* shared object which takes the reference count)?
* We believe SWAP_MAP_MAX cannot occur in Linux 2.4.
*
* How could swap count reach 0x7ffe ?
* There's no way to repeat a swap page within an mm
* (except in shmem, where it's the shared object which takes
* the reference count)?
* We believe SWAP_MAP_MAX cannot occur.(if occur, unsigned
* short is too small....)
* If that's wrong, then we should worry more about
* exit_mmap() and do_munmap() cases described above:
* we might be resetting SWAP_MAP_MAX too early here.
* We know "Undead"s can happen, they're okay, so don't
* report them; but do report if we reset SWAP_MAP_MAX.
*/
if (*swap_map == SWAP_MAP_MAX) {
/* We might release the lock_page() in unuse_mm(). */
if (!PageSwapCache(page) || page_private(page) != entry.val)
goto retry;
if (swap_count(*swap_map) == SWAP_MAP_MAX) {
spin_lock(&swap_lock);
*swap_map = 1;
*swap_map = encode_swapmap(0, true);
spin_unlock(&swap_lock);
reset_overflow = 1;
}
@ -1099,7 +1158,8 @@ static int try_to_unuse(unsigned int type)
* pages would be incorrect if swap supported "shared
* private" pages, but they are handled by tmpfs files.
*/
if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
if (swap_count(*swap_map) &&
PageDirty(page) && PageSwapCache(page)) {
struct writeback_control wbc = {
.sync_mode = WB_SYNC_NONE,
};
@ -1126,6 +1186,7 @@ static int try_to_unuse(unsigned int type)
* mark page dirty so shrink_page_list will preserve it.
*/
SetPageDirty(page);
retry:
unlock_page(page);
page_cache_release(page);
@ -1952,15 +2013,23 @@ void si_swapinfo(struct sysinfo *val)
*
* Note: if swap_map[] reaches SWAP_MAP_MAX the entries are treated as
* "permanent", but will be reclaimed by the next swapoff.
* Returns error code in following case.
* - success -> 0
* - swp_entry is invalid -> EINVAL
* - swp_entry is migration entry -> EINVAL
* - swap-cache reference is requested but there is already one. -> EEXIST
* - swap-cache reference is requested but the entry is not used. -> ENOENT
*/
int swap_duplicate(swp_entry_t entry)
static int __swap_duplicate(swp_entry_t entry, bool cache)
{
struct swap_info_struct * p;
unsigned long offset, type;
int result = 0;
int result = -EINVAL;
int count;
bool has_cache;
if (is_migration_entry(entry))
return 1;
return -EINVAL;
type = swp_type(entry);
if (type >= nr_swapfiles)
@ -1969,17 +2038,40 @@ int swap_duplicate(swp_entry_t entry)
offset = swp_offset(entry);
spin_lock(&swap_lock);
if (offset < p->max && p->swap_map[offset]) {
if (p->swap_map[offset] < SWAP_MAP_MAX - 1) {
p->swap_map[offset]++;
result = 1;
} else if (p->swap_map[offset] <= SWAP_MAP_MAX) {
if (unlikely(offset >= p->max))
goto unlock_out;
count = swap_count(p->swap_map[offset]);
has_cache = swap_has_cache(p->swap_map[offset]);
if (cache == SWAP_CACHE) { /* called for swapcache/swapin-readahead */
/* set SWAP_HAS_CACHE if there is no cache and entry is used */
if (!has_cache && count) {
p->swap_map[offset] = encode_swapmap(count, true);
result = 0;
} else if (has_cache) /* someone added cache */
result = -EEXIST;
else if (!count) /* no users */
result = -ENOENT;
} else if (count || has_cache) {
if (count < SWAP_MAP_MAX - 1) {
p->swap_map[offset] = encode_swapmap(count + 1,
has_cache);
result = 0;
} else if (count <= SWAP_MAP_MAX) {
if (swap_overflow++ < 5)
printk(KERN_WARNING "swap_dup: swap entry overflow\n");
p->swap_map[offset] = SWAP_MAP_MAX;
result = 1;
printk(KERN_WARNING
"swap_dup: swap entry overflow\n");
p->swap_map[offset] = encode_swapmap(SWAP_MAP_MAX,
has_cache);
result = 0;
}
}
} else
result = -ENOENT; /* unused swap entry */
unlock_out:
spin_unlock(&swap_lock);
out:
return result;
@ -1988,13 +2080,25 @@ bad_file:
printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
goto out;
}
/*
* increase reference count of swap entry by 1.
*/
void swap_duplicate(swp_entry_t entry)
{
__swap_duplicate(entry, SWAP_MAP);
}
/*
* @entry: swap entry for which we allocate swap cache.
*
* Called when allocating swap cache for exising swap entry,
* This can return error codes. Returns 0 at success.
* -EBUSY means there is a swap cache.
* Note: return code is different from swap_duplicate().
*/
int swapcache_prepare(swp_entry_t entry)
{
return swap_duplicate(entry);
return __swap_duplicate(entry, SWAP_CACHE);
}
@ -2035,7 +2139,7 @@ int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
/* Don't read in free or bad pages */
if (!si->swap_map[toff])
break;
if (si->swap_map[toff] == SWAP_MAP_BAD)
if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
break;
}
/* Count contiguous allocated slots below our target */
@ -2043,7 +2147,7 @@ int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
/* Don't read in free or bad pages */
if (!si->swap_map[toff])
break;
if (si->swap_map[toff] == SWAP_MAP_BAD)
if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
break;
}
spin_unlock(&swap_lock);