Messages in this thread Patch in this message |  | | | From | Nick Piggin <> | | Subject | [patch 1/6] mm: never ClearPageLRU released pages | | Date | Thu, 19 Jan 2006 20:22:51 +0100 (CET) |
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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 stabalise 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 synchroise against vmscan).
Signed-off-by: Nick Piggin <npiggin@suse.de>
Index: linux-2.6/mm/vmscan.c =================================================================== --- linux-2.6.orig/mm/vmscan.c +++ linux-2.6/mm/vmscan.c @@ -823,21 +823,25 @@ static int isolate_lru_pages(int nr_to_s 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; Index: linux-2.6/mm/swap.c =================================================================== --- linux-2.6.orig/mm/swap.c +++ linux-2.6/mm/swap.c @@ -206,17 +206,18 @@ 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; - spin_lock_irqsave(&zone->lru_lock, flags); - if (TestClearPageLRU(page)) + struct zone *zone = page_zone(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); @@ -242,27 +243,30 @@ void release_pages(struct page **pages, pagevec_init(&pages_to_free, cold); for (i = 0; i < nr; i++) { struct page *page = pages[i]; - struct zone *pagezone; 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) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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