On Wed, Mar 20, 2013 at 06:19:57PM +0000, Mel Gorman wrote: >The following problem was reported against a distribution kernel when >zone_reclaim was enabled but the same problem applies to the mainline >kernel. The reproduction case was as follows > >1. Run numactl -m +0 dd if=largefile of=/dev/null > This allocates a large number of clean pages in node 0 > >2. numactl -N +0 memhog 0.5*Mg > This start a memory-using application in node 0. > >The expected behaviour is that the clean pages get reclaimed and the >application uses node 0 for its memory. The observed behaviour was that >the memory for the memhog application was allocated off-node since commits >cd38b11 (mm: page allocator: initialise ZLC for first zone eligible for >zone_reclaim) and commit 76d3fbf (mm: page allocator: reconsider zones >for allocation after direct reclaim). > >The assumption of those patches was that it was always preferable to >allocate quickly than stall for long periods of time and they were >meant to take care that the zone was only marked full when necessary but >an important case was missed. > >In the allocator fast path, only the low watermarks are checked. If the >zones free pages are between the low and min watermark then allocations >from the allocators slow path will succeed. However, zone_reclaim >will only reclaim SWAP_CLUSTER_MAX or 1<<order pages. There is no >guarantee that this will meet the low watermark causing the zone to be >marked full prematurely. > >This patch will only mark the zone full after zone_reclaim if it the min >watermarks are checked or if page reclaim failed to make sufficient >progress. > >Reported-and-tested-by: Hedi Berriche <hedi@xxxxxxx> >Signed-off-by: Mel Gorman <mgorman@xxxxxxx> Reviewed-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx> >--- > mm/page_alloc.c | 17 ++++++++++++++++- > 1 file changed, 16 insertions(+), 1 deletion(-) > >diff --git a/mm/page_alloc.c b/mm/page_alloc.c >index 8fcced7..adce823 100644 >--- a/mm/page_alloc.c >+++ b/mm/page_alloc.c >@@ -1940,9 +1940,24 @@ zonelist_scan: > continue; > default: > /* did we reclaim enough */ >- if (!zone_watermark_ok(zone, order, mark, >+ if (zone_watermark_ok(zone, order, mark, > classzone_idx, alloc_flags)) >+ goto try_this_zone; >+ >+ /* >+ * Failed to reclaim enough to meet watermark. >+ * Only mark the zone full if checking the min >+ * watermark or if we failed to reclaim just >+ * 1<<order pages or else the page allocator >+ * fastpath will prematurely mark zones full >+ * when the watermark is between the low and >+ * min watermarks. >+ */ >+ if ((alloc_flags & ALLOC_WMARK_MIN) || >+ ret == ZONE_RECLAIM_SOME) > goto this_zone_full; >+ >+ continue; > } > } > > >-- >To unsubscribe, send a message with 'unsubscribe linux-mm' in >the body to majordomo@xxxxxxxxx. For more info on Linux MM, >see: http://www.linux-mm.org/ . >Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>