From 355cfa73ddff2fb8fa14e93bd94a057cc022512e Mon Sep 17 00:00:00 2001 From: KAMEZAWA Hiroyuki Date: Tue, 16 Jun 2009 15:32:53 -0700 Subject: mm: modify swap_map and add SWAP_HAS_CACHE flag 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 Tested-by: Daisuke Nishimura Cc: Balbir Singh Cc: Hugh Dickins Cc: Johannes Weiner Cc: Li Zefan Cc: Dhaval Giani Cc: YAMAMOTO Takashi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap_state.c | 5 +- mm/swapfile.c | 214 +++++++++++++++++++++++++++++++++++++++++--------------- 2 files changed, 163 insertions(+), 56 deletions(-) (limited to 'mm') diff --git a/mm/swap_state.c b/mm/swap_state.c index 19bdf3017a9..b9ca029673a 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -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+ err = swapcache_prepare(entry); + if (err == -EEXIST) /* seems racy */ + continue; + if (err) /* swp entry is obsolete ?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; /* diff --git a/mm/swapfile.c b/mm/swapfile.c index 3187079903f..0d7296971ad 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -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]; - - 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); + int count = swap_count(p->swap_map[offset]); + bool has_cache; + + 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); -- cgit v1.2.3-70-g09d2