From 56afe477df3cbbcd656682d0355ef7d9eb8bdd81 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Wed, 11 Sep 2013 14:22:32 -0700 Subject: mm: munlock: bypass per-cpu pvec for putback_lru_page MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit After introducing batching by pagevecs into munlock_vma_range(), we can further improve performance by bypassing the copying into per-cpu pagevec and the get_page/put_page pair associated with that. Instead we perform LRU putback directly from our pagevec. However, this is possible only for single-mapped pages that are evictable after munlock. Unevictable pages require rechecking after putting on the unevictable list, so for those we fallback to putback_lru_page(), hich handles that. After this patch, a 13% speedup was measured for munlocking a 56GB large memory area with THP disabled. [akpm@linux-foundation.org:clarify comment] Signed-off-by: Vlastimil Babka Reviewed-by: Jörn Engel Acked-by: Mel Gorman Cc: Michel Lespinasse Cc: Hugh Dickins Cc: Rik van Riel Cc: Johannes Weiner Cc: Michal Hocko Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mlock.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 69 insertions(+), 4 deletions(-) (limited to 'mm/mlock.c') diff --git a/mm/mlock.c b/mm/mlock.c index b1a7c8007c89..abdc612b042d 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -226,6 +226,52 @@ static int __mlock_posix_error_return(long retval) return retval; } +/* + * Prepare page for fast batched LRU putback via putback_lru_evictable_pagevec() + * + * The fast path is available only for evictable pages with single mapping. + * Then we can bypass the per-cpu pvec and get better performance. + * when mapcount > 1 we need try_to_munlock() which can fail. + * when !page_evictable(), we need the full redo logic of putback_lru_page to + * avoid leaving evictable page in unevictable list. + * + * In case of success, @page is added to @pvec and @pgrescued is incremented + * in case that the page was previously unevictable. @page is also unlocked. + */ +static bool __putback_lru_fast_prepare(struct page *page, struct pagevec *pvec, + int *pgrescued) +{ + VM_BUG_ON(PageLRU(page)); + VM_BUG_ON(!PageLocked(page)); + + if (page_mapcount(page) <= 1 && page_evictable(page)) { + pagevec_add(pvec, page); + if (TestClearPageUnevictable(page)) + (*pgrescued)++; + unlock_page(page); + return true; + } + + return false; +} + +/* + * Putback multiple evictable pages to the LRU + * + * Batched putback of evictable pages that bypasses the per-cpu pvec. Some of + * the pages might have meanwhile become unevictable but that is OK. + */ +static void __putback_lru_fast(struct pagevec *pvec, int pgrescued) +{ + count_vm_events(UNEVICTABLE_PGMUNLOCKED, pagevec_count(pvec)); + /* + *__pagevec_lru_add() calls release_pages() so we don't call + * put_page() explicitly + */ + __pagevec_lru_add(pvec); + count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued); +} + /* * Munlock a batch of pages from the same zone * @@ -242,6 +288,8 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone) int i; int nr = pagevec_count(pvec); int delta_munlocked = -nr; + struct pagevec pvec_putback; + int pgrescued = 0; /* Phase 1: page isolation */ spin_lock_irq(&zone->lru_lock); @@ -279,17 +327,34 @@ skip_munlock: __mod_zone_page_state(zone, NR_MLOCK, delta_munlocked); spin_unlock_irq(&zone->lru_lock); - /* Phase 2: page munlock and putback */ + /* Phase 2: page munlock */ + pagevec_init(&pvec_putback, 0); for (i = 0; i < nr; i++) { struct page *page = pvec->pages[i]; if (page) { lock_page(page); - __munlock_isolated_page(page); - unlock_page(page); - put_page(page); /* pin from follow_page_mask() */ + if (!__putback_lru_fast_prepare(page, &pvec_putback, + &pgrescued)) { + /* Slow path */ + __munlock_isolated_page(page); + unlock_page(page); + } } } + + /* Phase 3: page putback for pages that qualified for the fast path */ + if (pagevec_count(&pvec_putback)) + __putback_lru_fast(&pvec_putback, pgrescued); + + /* Phase 4: put_page to return pin from follow_page_mask() */ + for (i = 0; i < nr; i++) { + struct page *page = pvec->pages[i]; + + if (page) + put_page(page); + } + pagevec_reinit(pvec); } -- cgit v1.2.3-59-g8ed1b