From 73ce02e96fe34a983199a9855b2ae738f960a6ee Mon Sep 17 00:00:00 2001 From: KOSAKI Motohiro Date: Tue, 6 Jan 2009 14:40:33 -0800 Subject: [PATCH] mm: stop kswapd's infinite loop at high order allocation Wassim Dagash reported following kswapd infinite loop problem. kswapd runs in some infinite loop trying to swap until order 10 of zone highmem is OK.... kswapd will continue to try to balance order 10 of zone highmem forever (or until someone release a very large chunk of highmem). For non order-0 allocations, the system may never be balanced due to fragmentation but kswapd should not infinitely loop as a result. Instead, recheck all watermarks at order-0 as they are the most important. If watermarks are ok, kswapd will go back to sleep. [akpm@linux-foundation.org: fix comment] Reported-by: wassim dagash Signed-off-by: KOSAKI Motohiro Reviewed-by: Nick Piggin Signed-off-by: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmscan.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/mm/vmscan.c b/mm/vmscan.c index 5daf606e0a35..b07c48b09a93 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1867,6 +1867,23 @@ out: try_to_freeze(); + /* + * Fragmentation may mean that the system cannot be + * rebalanced for high-order allocations in all zones. + * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX, + * it means the zones have been fully scanned and are still + * not balanced. For high-order allocations, there is + * little point trying all over again as kswapd may + * infinite loop. + * + * Instead, recheck all watermarks at order-0 as they + * are the most important. If watermarks are ok, kswapd will go + * back to sleep. High-order users can still perform direct + * reclaim if they wish. + */ + if (sc.nr_reclaimed < SWAP_CLUSTER_MAX) + order = sc.order = 0; + goto loop_again; } -- 2.39.5