On Wed 20-03-13 18:19:57, 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: Michal Hocko <mhocko@xxxxxxx> > --- > 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; > } > } > -- Michal Hocko SUSE Labs -- 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>