From ec8acf20afb8534ed511f6613dd2226b9e301010 Mon Sep 17 00:00:00 2001 From: Shaohua Li Date: Fri, 22 Feb 2013 16:34:38 -0800 Subject: swap: add per-partition lock for swapfile swap_lock is heavily contended when I test swap to 3 fast SSD (even slightly slower than swap to 2 such SSD). The main contention comes from swap_info_get(). This patch tries to fix the gap with adding a new per-partition lock. Global data like nr_swapfiles, total_swap_pages, least_priority and swap_list are still protected by swap_lock. nr_swap_pages is an atomic now, it can be changed without swap_lock. In theory, it's possible get_swap_page() finds no swap pages but actually there are free swap pages. But sounds not a big problem. Accessing partition specific data (like scan_swap_map and so on) is only protected by swap_info_struct.lock. Changing swap_info_struct.flags need hold swap_lock and swap_info_struct.lock, because scan_scan_map() will check it. read the flags is ok with either the locks hold. If both swap_lock and swap_info_struct.lock must be hold, we always hold the former first to avoid deadlock. swap_entry_free() can change swap_list. To delete that code, we add a new highest_priority_index. Whenever get_swap_page() is called, we check it. If it's valid, we use it. It's a pity get_swap_page() still holds swap_lock(). But in practice, swap_lock() isn't heavily contended in my test with this patch (or I can say there are other much more heavier bottlenecks like TLB flush). And BTW, looks get_swap_page() doesn't really need the lock. We never free swap_info[] and we check SWAP_WRITEOK flag. The only risk without the lock is we could swapout to some low priority swap, but we can quickly recover after several rounds of swap, so sounds not a big deal to me. But I'd prefer to fix this if it's a real problem. "swap: make each swap partition have one address_space" improved the swapout speed from 1.7G/s to 2G/s. This patch further improves the speed to 2.3G/s, so around 15% improvement. It's a multi-process test, so TLB flush isn't the biggest bottleneck before the patches. [arnd@arndb.de: fix it for nommu] [hughd@google.com: add missing unlock] [minchan@kernel.org: get rid of lockdep whinge on sys_swapon] Signed-off-by: Shaohua Li Cc: Hugh Dickins Cc: Rik van Riel Cc: Minchan Kim Cc: Greg Kroah-Hartman Cc: Seth Jennings Cc: Konrad Rzeszutek Wilk Cc: Xiao Guangrong Cc: Dan Magenheimer Cc: Stephen Rothwell Signed-off-by: Arnd Bergmann Signed-off-by: Hugh Dickins Signed-off-by: Minchan Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swapfile.c | 154 ++++++++++++++++++++++++++++++++++++++++------------------ 1 file changed, 108 insertions(+), 46 deletions(-) (limited to 'mm/swapfile.c') diff --git a/mm/swapfile.c b/mm/swapfile.c index e51864e6fe8b..9b51266413cd 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -47,9 +47,11 @@ static sector_t map_swap_entry(swp_entry_t, struct block_device**); DEFINE_SPINLOCK(swap_lock); static unsigned int nr_swapfiles; -long nr_swap_pages; +atomic_long_t nr_swap_pages; +/* protected with swap_lock. reading in vm_swap_full() doesn't need lock */ long total_swap_pages; static int least_priority; +static atomic_t highest_priority_index = ATOMIC_INIT(-1); static const char Bad_file[] = "Bad swap file entry "; static const char Unused_file[] = "Unused swap file entry "; @@ -223,7 +225,7 @@ static unsigned long scan_swap_map(struct swap_info_struct *si, si->lowest_alloc = si->max; si->highest_alloc = 0; } - spin_unlock(&swap_lock); + spin_unlock(&si->lock); /* * If seek is expensive, start searching for new cluster from @@ -242,7 +244,7 @@ static unsigned long scan_swap_map(struct swap_info_struct *si, if (si->swap_map[offset]) last_in_cluster = offset + SWAPFILE_CLUSTER; else if (offset == last_in_cluster) { - spin_lock(&swap_lock); + spin_lock(&si->lock); offset -= SWAPFILE_CLUSTER - 1; si->cluster_next = offset; si->cluster_nr = SWAPFILE_CLUSTER - 1; @@ -263,7 +265,7 @@ static unsigned long scan_swap_map(struct swap_info_struct *si, if (si->swap_map[offset]) last_in_cluster = offset + SWAPFILE_CLUSTER; else if (offset == last_in_cluster) { - spin_lock(&swap_lock); + spin_lock(&si->lock); offset -= SWAPFILE_CLUSTER - 1; si->cluster_next = offset; si->cluster_nr = SWAPFILE_CLUSTER - 1; @@ -277,7 +279,7 @@ static unsigned long scan_swap_map(struct swap_info_struct *si, } offset = scan_base; - spin_lock(&swap_lock); + spin_lock(&si->lock); si->cluster_nr = SWAPFILE_CLUSTER - 1; si->lowest_alloc = 0; } @@ -293,9 +295,9 @@ checks: /* reuse swap entry of cache-only swap if not busy. */ if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) { int swap_was_freed; - spin_unlock(&swap_lock); + spin_unlock(&si->lock); swap_was_freed = __try_to_reclaim_swap(si, offset); - spin_lock(&swap_lock); + spin_lock(&si->lock); /* entry was freed successfully, try to use this again */ if (swap_was_freed) goto checks; @@ -335,13 +337,13 @@ checks: si->lowest_alloc <= last_in_cluster) last_in_cluster = si->lowest_alloc - 1; si->flags |= SWP_DISCARDING; - spin_unlock(&swap_lock); + spin_unlock(&si->lock); if (offset < last_in_cluster) discard_swap_cluster(si, offset, last_in_cluster - offset + 1); - spin_lock(&swap_lock); + spin_lock(&si->lock); si->lowest_alloc = 0; si->flags &= ~SWP_DISCARDING; @@ -355,10 +357,10 @@ checks: * could defer that delay until swap_writepage, * but it's easier to keep this self-contained. */ - spin_unlock(&swap_lock); + spin_unlock(&si->lock); wait_on_bit(&si->flags, ilog2(SWP_DISCARDING), wait_for_discard, TASK_UNINTERRUPTIBLE); - spin_lock(&swap_lock); + spin_lock(&si->lock); } else { /* * Note pages allocated by racing tasks while @@ -374,14 +376,14 @@ checks: return offset; scan: - spin_unlock(&swap_lock); + spin_unlock(&si->lock); while (++offset <= si->highest_bit) { if (!si->swap_map[offset]) { - spin_lock(&swap_lock); + spin_lock(&si->lock); goto checks; } if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) { - spin_lock(&swap_lock); + spin_lock(&si->lock); goto checks; } if (unlikely(--latency_ration < 0)) { @@ -392,11 +394,11 @@ scan: offset = si->lowest_bit; while (++offset < scan_base) { if (!si->swap_map[offset]) { - spin_lock(&swap_lock); + spin_lock(&si->lock); goto checks; } if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) { - spin_lock(&swap_lock); + spin_lock(&si->lock); goto checks; } if (unlikely(--latency_ration < 0)) { @@ -404,7 +406,7 @@ scan: latency_ration = LATENCY_LIMIT; } } - spin_lock(&swap_lock); + spin_lock(&si->lock); no_page: si->flags -= SWP_SCANNING; @@ -417,13 +419,34 @@ swp_entry_t get_swap_page(void) pgoff_t offset; int type, next; int wrapped = 0; + int hp_index; spin_lock(&swap_lock); - if (nr_swap_pages <= 0) + if (atomic_long_read(&nr_swap_pages) <= 0) goto noswap; - nr_swap_pages--; + atomic_long_dec(&nr_swap_pages); for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) { + hp_index = atomic_xchg(&highest_priority_index, -1); + /* + * highest_priority_index records current highest priority swap + * type which just frees swap entries. If its priority is + * higher than that of swap_list.next swap type, we use it. It + * isn't protected by swap_lock, so it can be an invalid value + * if the corresponding swap type is swapoff. We double check + * the flags here. It's even possible the swap type is swapoff + * and swapon again and its priority is changed. In such rare + * case, low prority swap type might be used, but eventually + * high priority swap will be used after several rounds of + * swap. + */ + if (hp_index != -1 && hp_index != type && + swap_info[type]->prio < swap_info[hp_index]->prio && + (swap_info[hp_index]->flags & SWP_WRITEOK)) { + type = hp_index; + swap_list.next = type; + } + si = swap_info[type]; next = si->next; if (next < 0 || @@ -432,22 +455,29 @@ swp_entry_t get_swap_page(void) wrapped++; } - if (!si->highest_bit) + spin_lock(&si->lock); + if (!si->highest_bit) { + spin_unlock(&si->lock); continue; - if (!(si->flags & SWP_WRITEOK)) + } + if (!(si->flags & SWP_WRITEOK)) { + spin_unlock(&si->lock); continue; + } swap_list.next = next; + + spin_unlock(&swap_lock); /* This is called for allocating swap entry for cache */ offset = scan_swap_map(si, SWAP_HAS_CACHE); - if (offset) { - spin_unlock(&swap_lock); + spin_unlock(&si->lock); + if (offset) return swp_entry(type, offset); - } + spin_lock(&swap_lock); next = swap_list.next; } - nr_swap_pages++; + atomic_long_inc(&nr_swap_pages); noswap: spin_unlock(&swap_lock); return (swp_entry_t) {0}; @@ -459,19 +489,19 @@ swp_entry_t get_swap_page_of_type(int type) struct swap_info_struct *si; pgoff_t offset; - spin_lock(&swap_lock); si = swap_info[type]; + spin_lock(&si->lock); if (si && (si->flags & SWP_WRITEOK)) { - nr_swap_pages--; + atomic_long_dec(&nr_swap_pages); /* This is called for allocating swap entry, not cache */ offset = scan_swap_map(si, 1); if (offset) { - spin_unlock(&swap_lock); + spin_unlock(&si->lock); return swp_entry(type, offset); } - nr_swap_pages++; + atomic_long_inc(&nr_swap_pages); } - spin_unlock(&swap_lock); + spin_unlock(&si->lock); return (swp_entry_t) {0}; } @@ -493,7 +523,7 @@ static struct swap_info_struct *swap_info_get(swp_entry_t entry) goto bad_offset; if (!p->swap_map[offset]) goto bad_free; - spin_lock(&swap_lock); + spin_lock(&p->lock); return p; bad_free: @@ -511,6 +541,27 @@ out: return NULL; } +/* + * This swap type frees swap entry, check if it is the highest priority swap + * type which just frees swap entry. get_swap_page() uses + * highest_priority_index to search highest priority swap type. The + * swap_info_struct.lock can't protect us if there are multiple swap types + * active, so we use atomic_cmpxchg. + */ +static void set_highest_priority_index(int type) +{ + int old_hp_index, new_hp_index; + + do { + old_hp_index = atomic_read(&highest_priority_index); + if (old_hp_index != -1 && + swap_info[old_hp_index]->prio >= swap_info[type]->prio) + break; + new_hp_index = type; + } while (atomic_cmpxchg(&highest_priority_index, + old_hp_index, new_hp_index) != old_hp_index); +} + static unsigned char swap_entry_free(struct swap_info_struct *p, swp_entry_t entry, unsigned char usage) { @@ -553,10 +604,8 @@ static unsigned char swap_entry_free(struct swap_info_struct *p, p->lowest_bit = offset; if (offset > p->highest_bit) p->highest_bit = offset; - if (swap_list.next >= 0 && - p->prio > swap_info[swap_list.next]->prio) - swap_list.next = p->type; - nr_swap_pages++; + set_highest_priority_index(p->type); + atomic_long_inc(&nr_swap_pages); p->inuse_pages--; frontswap_invalidate_page(p->type, offset); if (p->flags & SWP_BLKDEV) { @@ -581,7 +630,7 @@ void swap_free(swp_entry_t entry) p = swap_info_get(entry); if (p) { swap_entry_free(p, entry, 1); - spin_unlock(&swap_lock); + spin_unlock(&p->lock); } } @@ -598,7 +647,7 @@ void swapcache_free(swp_entry_t entry, struct page *page) count = swap_entry_free(p, entry, SWAP_HAS_CACHE); if (page) mem_cgroup_uncharge_swapcache(page, entry, count != 0); - spin_unlock(&swap_lock); + spin_unlock(&p->lock); } } @@ -617,7 +666,7 @@ int page_swapcount(struct page *page) p = swap_info_get(entry); if (p) { count = swap_count(p->swap_map[swp_offset(entry)]); - spin_unlock(&swap_lock); + spin_unlock(&p->lock); } return count; } @@ -706,7 +755,7 @@ int free_swap_and_cache(swp_entry_t entry) page = NULL; } } - spin_unlock(&swap_lock); + spin_unlock(&p->lock); } if (page) { /* @@ -804,11 +853,13 @@ unsigned int count_swap_pages(int type, int free) if ((unsigned int)type < nr_swapfiles) { struct swap_info_struct *sis = swap_info[type]; + spin_lock(&sis->lock); if (sis->flags & SWP_WRITEOK) { n = sis->pages; if (free) n -= sis->inuse_pages; } + spin_unlock(&sis->lock); } spin_unlock(&swap_lock); return n; @@ -1457,7 +1508,7 @@ static void _enable_swap_info(struct swap_info_struct *p, int prio, p->swap_map = swap_map; frontswap_map_set(p, frontswap_map); p->flags |= SWP_WRITEOK; - nr_swap_pages += p->pages; + atomic_long_add(p->pages, &nr_swap_pages); total_swap_pages += p->pages; /* insert swap space into swap_list: */ @@ -1479,15 +1530,19 @@ static void enable_swap_info(struct swap_info_struct *p, int prio, unsigned long *frontswap_map) { spin_lock(&swap_lock); + spin_lock(&p->lock); _enable_swap_info(p, prio, swap_map, frontswap_map); frontswap_init(p->type); + spin_unlock(&p->lock); spin_unlock(&swap_lock); } static void reinsert_swap_info(struct swap_info_struct *p) { spin_lock(&swap_lock); + spin_lock(&p->lock); _enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p)); + spin_unlock(&p->lock); spin_unlock(&swap_lock); } @@ -1547,14 +1602,16 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) /* just pick something that's safe... */ swap_list.next = swap_list.head; } + spin_lock(&p->lock); if (p->prio < 0) { for (i = p->next; i >= 0; i = swap_info[i]->next) swap_info[i]->prio = p->prio--; least_priority++; } - nr_swap_pages -= p->pages; + atomic_long_sub(p->pages, &nr_swap_pages); total_swap_pages -= p->pages; p->flags &= ~SWP_WRITEOK; + spin_unlock(&p->lock); spin_unlock(&swap_lock); set_current_oom_origin(); @@ -1573,14 +1630,17 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) mutex_lock(&swapon_mutex); spin_lock(&swap_lock); + spin_lock(&p->lock); drain_mmlist(); /* wait for anyone still in scan_swap_map */ p->highest_bit = 0; /* cuts scans short */ while (p->flags >= SWP_SCANNING) { + spin_unlock(&p->lock); spin_unlock(&swap_lock); schedule_timeout_uninterruptible(1); spin_lock(&swap_lock); + spin_lock(&p->lock); } swap_file = p->swap_file; @@ -1590,6 +1650,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) p->swap_map = NULL; p->flags = 0; frontswap_invalidate_area(type); + spin_unlock(&p->lock); spin_unlock(&swap_lock); mutex_unlock(&swapon_mutex); vfree(swap_map); @@ -1795,6 +1856,7 @@ static struct swap_info_struct *alloc_swap_info(void) p->flags = SWP_USED; p->next = -1; spin_unlock(&swap_lock); + spin_lock_init(&p->lock); return p; } @@ -2117,7 +2179,7 @@ void si_swapinfo(struct sysinfo *val) if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK)) nr_to_be_unused += si->inuse_pages; } - val->freeswap = nr_swap_pages + nr_to_be_unused; + val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused; val->totalswap = total_swap_pages + nr_to_be_unused; spin_unlock(&swap_lock); } @@ -2150,7 +2212,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage) p = swap_info[type]; offset = swp_offset(entry); - spin_lock(&swap_lock); + spin_lock(&p->lock); if (unlikely(offset >= p->max)) goto unlock_out; @@ -2185,7 +2247,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage) p->swap_map[offset] = count | has_cache; unlock_out: - spin_unlock(&swap_lock); + spin_unlock(&p->lock); out: return err; @@ -2310,7 +2372,7 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask) } if (!page) { - spin_unlock(&swap_lock); + spin_unlock(&si->lock); return -ENOMEM; } @@ -2358,7 +2420,7 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask) list_add_tail(&page->lru, &head->lru); page = NULL; /* now it's attached, don't free it */ out: - spin_unlock(&swap_lock); + spin_unlock(&si->lock); outer: if (page) __free_page(page); -- cgit