From: Mel Gorman Subject: [PATCH 2/3] mm: Ensure that mark_page_accessed moves pages to the active list Date: Mon, 29 Apr 2013 17:31:58 +0100 Message-ID: <1367253119-6461-3-git-send-email-mgorman@suse.de> References: <1367253119-6461-1-git-send-email-mgorman@suse.de> Cc: Theodore Tso , Andrew Morton , Hugh Dickins , Rik van Riel , Johannes Weiner , Bernd Schubert , David Howells , Trond Myklebust , Linux-fsdevel , Linux-ext4 , LKML , Linux-mm , Mel Gorman To: Alexey Lyahkov , Andrew Perepechko , Robin Dong Return-path: In-Reply-To: <1367253119-6461-1-git-send-email-mgorman@suse.de> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org If a page is on a pagevec then it is !PageLRU and mark_page_accessed() may fail to move a page to the active list as expected. Now that the LRU is selected at LRU drain time, mark pages PageActive if they are on a pagevec so it gets moved to the correct list at LRU drain time. Using a debugging patch it was found that for a simple git checkout based workload that pages were never added to the active file list in practice but with this patch applied they are. before after LRU Add Active File 0 757121 LRU Add Active Anon 2678833 2633924 LRU Add Inactive File 8821711 8085543 LRU Add Inactive Anon 183 200 The question to consider is if this is universally safe. If the page was isolated for reclaim and there is a parallel mark_page_accessed() then vmscan.c will get upset when it finds an isolated PageActive page. Similarly a potential race exists between a per-cpu drain on a pagevec list and an activation on a remote CPU. lru_add_drain_cpu __pagevec_lru_add lru = page_lru(page); mark_page_accessed if (PageLRU(page)) activate_page else SetPageActive SetPageLRU(page); add_page_to_lru_list(page, lruvec, lru); A PageActive page is now added to the inactivate list. While this looks strange, I think it is sufficiently harmless that additional barriers to address the case is not justified. Unfortunately, while I never witnessed it myself, these parallel updates potentially trigger defensive DEBUG_VM checks on PageActive and hence they are removed by this patch. Signed-off-by: Mel Gorman --- mm/swap.c | 18 ++++++++++++------ mm/vmscan.c | 3 --- 2 files changed, 12 insertions(+), 9 deletions(-) diff --git a/mm/swap.c b/mm/swap.c index 80fbc37..2a10d08 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -437,8 +437,17 @@ void activate_page(struct page *page) void mark_page_accessed(struct page *page) { if (!PageActive(page) && !PageUnevictable(page) && - PageReferenced(page) && PageLRU(page)) { - activate_page(page); + PageReferenced(page)) { + + /* + * If the page is on the LRU, promote immediately. Otherwise, + * assume the page is on a pagevec, mark it active and it'll + * be moved to the active LRU on the next drain + */ + if (PageLRU(page)) + activate_page(page); + else + SetPageActive(page); ClearPageReferenced(page); } else if (!PageReferenced(page)) { SetPageReferenced(page); @@ -478,11 +487,8 @@ EXPORT_SYMBOL(__lru_cache_add); */ void lru_cache_add_lru(struct page *page, enum lru_list lru) { - if (PageActive(page)) { + if (PageActive(page)) VM_BUG_ON(PageUnevictable(page)); - } else if (PageUnevictable(page)) { - VM_BUG_ON(PageActive(page)); - } VM_BUG_ON(PageLRU(page)); __lru_cache_add(page, lru); diff --git a/mm/vmscan.c b/mm/vmscan.c index 88c5fed..751b897 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -704,7 +704,6 @@ static unsigned long shrink_page_list(struct list_head *page_list, if (!trylock_page(page)) goto keep; - VM_BUG_ON(PageActive(page)); VM_BUG_ON(page_zone(page) != zone); sc->nr_scanned++; @@ -935,7 +934,6 @@ activate_locked: /* Not a candidate for swapping, so reclaim swap space. */ if (PageSwapCache(page) && vm_swap_full()) try_to_free_swap(page); - VM_BUG_ON(PageActive(page)); SetPageActive(page); pgactivate++; keep_locked: @@ -3488,7 +3486,6 @@ void check_move_unevictable_pages(struct page **pages, int nr_pages) if (page_evictable(page)) { enum lru_list lru = page_lru_base_type(page); - VM_BUG_ON(PageActive(page)); ClearPageUnevictable(page); del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE); add_page_to_lru_list(page, lruvec, lru); -- 1.8.1.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org