From 46453a6e194a8c55fe6cf3dc8e1c4f24e2abc013 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Wed, 22 Mar 2006 00:07:58 -0800 Subject: [PATCH] [PATCH] mm: never ClearPageLRU released pages If vmscan finds a zero refcount page on the lru list, never ClearPageLRU it. This means the release code need not hold ->lru_lock to stabilise PageLRU, so that lock may be skipped entirely when releasing !PageLRU pages (because we know PageLRU won't have been temporarily cleared by vmscan, which was previously guaranteed by holding the lock to synchronise against vmscan). Signed-off-by: Nick Piggin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap.c | 52 +++++++++++++++++++++++++++------------------------- mm/vmscan.c | 18 +++++++++++------- 2 files changed, 38 insertions(+), 32 deletions(-) diff --git a/mm/swap.c b/mm/swap.c index b524ea90bd..3045a0f4c4 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -209,19 +209,18 @@ int lru_add_drain_all(void) */ void fastcall __page_cache_release(struct page *page) { - unsigned long flags; - struct zone *zone = page_zone(page); + if (PageLRU(page)) { + unsigned long flags; + struct zone *zone = page_zone(page); - spin_lock_irqsave(&zone->lru_lock, flags); - if (TestClearPageLRU(page)) + spin_lock_irqsave(&zone->lru_lock, flags); + if (!TestClearPageLRU(page)) + BUG(); del_page_from_lru(zone, page); - if (page_count(page) != 0) - page = NULL; - spin_unlock_irqrestore(&zone->lru_lock, flags); - if (page) - free_hot_page(page); + spin_unlock_irqrestore(&zone->lru_lock, flags); + } + free_hot_page(page); } - EXPORT_SYMBOL(__page_cache_release); /* @@ -245,7 +244,6 @@ void release_pages(struct page **pages, int nr, int cold) pagevec_init(&pages_to_free, cold); for (i = 0; i < nr; i++) { struct page *page = pages[i]; - struct zone *pagezone; if (unlikely(PageCompound(page))) { if (zone) { @@ -259,23 +257,27 @@ void release_pages(struct page **pages, int nr, int cold) if (!put_page_testzero(page)) continue; - pagezone = page_zone(page); - if (pagezone != zone) { - if (zone) - spin_unlock_irq(&zone->lru_lock); - zone = pagezone; - spin_lock_irq(&zone->lru_lock); - } - if (TestClearPageLRU(page)) + if (PageLRU(page)) { + struct zone *pagezone = page_zone(page); + if (pagezone != zone) { + if (zone) + spin_unlock_irq(&zone->lru_lock); + zone = pagezone; + spin_lock_irq(&zone->lru_lock); + } + if (!TestClearPageLRU(page)) + BUG(); del_page_from_lru(zone, page); - if (page_count(page) == 0) { - if (!pagevec_add(&pages_to_free, page)) { + } + + if (!pagevec_add(&pages_to_free, page)) { + if (zone) { spin_unlock_irq(&zone->lru_lock); - __pagevec_free(&pages_to_free); - pagevec_reinit(&pages_to_free); - zone = NULL; /* No lock is held */ + zone = NULL; } - } + __pagevec_free(&pages_to_free); + pagevec_reinit(&pages_to_free); + } } if (zone) spin_unlock_irq(&zone->lru_lock); diff --git a/mm/vmscan.c b/mm/vmscan.c index 4fe7e3aa02..acb7611cd5 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1085,21 +1085,25 @@ static int isolate_lru_pages(int nr_to_scan, struct list_head *src, page = lru_to_page(src); prefetchw_prev_lru_page(page, src, flags); - if (!TestClearPageLRU(page)) - BUG(); list_del(&page->lru); - if (get_page_testone(page)) { + if (unlikely(get_page_testone(page))) { /* * It is being freed elsewhere */ __put_page(page); - SetPageLRU(page); list_add(&page->lru, src); continue; - } else { - list_add(&page->lru, dst); - nr_taken++; } + + /* + * Be careful not to clear PageLRU until after we're sure + * the page is not being freed elsewhere -- the page release + * code relies on it. + */ + if (!TestClearPageLRU(page)) + BUG(); + list_add(&page->lru, dst); + nr_taken++; } *scanned = scan; -- 2.39.2