From 22d82c7586eb492067805dd781f84f5a94133357 Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Tue, 24 May 2011 17:11:11 -0700 Subject: [PATCH] mm: vmscan: correctly check if reclaimer should schedule during shrink_slab commit f06590bd718ed950c98828e30ef93204028f3210 upstream. It has been reported on some laptops that kswapd is consuming large amounts of CPU and not being scheduled when SLUB is enabled during large amounts of file copying. It is expected that this is due to kswapd missing every cond_resched() point because; shrink_page_list() calls cond_resched() if inactive pages were isolated which in turn may not happen if all_unreclaimable is set in shrink_zones(). If for whatver reason, all_unreclaimable is set on all zones, we can miss calling cond_resched(). balance_pgdat() only calls cond_resched if the zones are not balanced. For a high-order allocation that is balanced, it checks order-0 again. During that window, order-0 might have become unbalanced so it loops again for order-0 and returns that it was reclaiming for order-0 to kswapd(). It can then find that a caller has rewoken kswapd for a high-order and re-enters balance_pgdat() without ever calling cond_resched(). shrink_slab only calls cond_resched() if we are reclaiming slab pages. If there are a large number of direct reclaimers, the shrinker_rwsem can be contended and prevent kswapd calling cond_resched(). This patch modifies the shrink_slab() case. If the semaphore is contended, the caller will still check cond_resched(). After each successful call into a shrinker, the check for cond_resched() remains in case one shrinker is particularly slow. [mgorman@suse.de: preserve call to cond_resched after each call into shrinker] Signed-off-by: Mel Gorman Signed-off-by: Minchan Kim Cc: Rik van Riel Cc: Johannes Weiner Cc: Wu Fengguang Cc: James Bottomley Tested-by: Colin King Cc: Raghavendra D Prabhu Cc: Jan Kara Cc: Chris Mason Cc: Christoph Lameter Cc: Pekka Enberg Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/vmscan.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 1aa262b1d5e2..cc1470bc9b8d 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -230,8 +230,11 @@ unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask, if (scanned == 0) scanned = SWAP_CLUSTER_MAX; - if (!down_read_trylock(&shrinker_rwsem)) - return 1; /* Assume we'll be able to shrink next time */ + if (!down_read_trylock(&shrinker_rwsem)) { + /* Assume we'll be able to shrink next time */ + ret = 1; + goto out; + } list_for_each_entry(shrinker, &shrinker_list, list) { unsigned long long delta; @@ -282,6 +285,8 @@ unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask, shrinker->nr += total_scan; } up_read(&shrinker_rwsem); +out: + cond_resched(); return ret; } -- 2.39.5