From 7ff4751a6e1d3dbb9231b1228d8a6ee029982c5f Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Wed, 28 Sep 2011 10:50:07 +1000 Subject: [PATCH] mm: vmscan: do not writeback filesystem pages in kswapd except in high priority It is preferable that no dirty pages are dispatched for cleaning from the page reclaim path. At normal priorities, this patch prevents kswapd writing pages. However, page reclaim does have a requirement that pages be freed in a particular zone. If it is failing to make sufficient progress (reclaiming < SWAP_CLUSTER_MAX at any priority priority), the priority is raised to scan more pages. A priority of DEF_PRIORITY - 3 is considered to be the point where kswapd is getting into trouble reclaiming pages. If this priority is reached, kswapd will dispatch pages for writing. Signed-off-by: Mel Gorman Reviewed-by: Minchan Kim Cc: Dave Chinner Cc: Christoph Hellwig Cc: Johannes Weiner Cc: Wu Fengguang Cc: Jan Kara Cc: Rik van Riel Cc: Mel Gorman Cc: Alex Elder Cc: Theodore Ts'o Cc: Chris Mason Cc: Dave Hansen Signed-off-by: Andrew Morton <> --- mm/vmscan.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 5c596654bd37..15e3a29fdb23 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -750,7 +750,8 @@ static noinline_for_stack void free_page_list(struct list_head *free_pages) */ static unsigned long shrink_page_list(struct list_head *page_list, struct zone *zone, - struct scan_control *sc) + struct scan_control *sc, + int priority) { LIST_HEAD(ret_pages); LIST_HEAD(free_pages); @@ -856,9 +857,11 @@ static unsigned long shrink_page_list(struct list_head *page_list, /* * Only kswapd can writeback filesystem pages to - * avoid risk of stack overflow + * avoid risk of stack overflow but do not writeback + * unless under significant pressure. */ - if (page_is_file_cache(page) && !current_is_kswapd()) { + if (page_is_file_cache(page) && + (!current_is_kswapd() || priority >= DEF_PRIORITY - 2)) { inc_zone_page_state(page, NR_VMSCAN_WRITE_SKIP); goto keep_locked; } @@ -1509,12 +1512,12 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone, spin_unlock_irq(&zone->lru_lock); - nr_reclaimed = shrink_page_list(&page_list, zone, sc); + nr_reclaimed = shrink_page_list(&page_list, zone, sc, priority); /* Check if we should syncronously wait for writeback */ if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) { set_reclaim_mode(priority, sc, true); - nr_reclaimed += shrink_page_list(&page_list, zone, sc); + nr_reclaimed += shrink_page_list(&page_list, zone, sc, priority); } local_irq_disable(); -- 2.39.5