vmscan: limit direct reclaim for higher order allocations

When suffering from memory fragmentation due to unfreeable pages, THP page
faults will repeatedly try to compact memory.  Due to the unfreeable
pages, compaction fails.

Needless to say, at that point page reclaim also fails to create free
contiguous 2MB areas.  However, that doesn't stop the current code from
trying, over and over again, and freeing a minimum of 4MB (2UL <<
sc->order pages) at every single invocation.

This resulted in my 12GB system having 2-3GB free memory, a corresponding
amount of used swap and very sluggish response times.

This can be avoided by having the direct reclaim code not reclaim from
zones that already have plenty of free memory available for compaction.

If compaction still fails due to unmovable memory, doing additional
reclaim will only hurt the system, not help.

Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Johannes Weiner <jweiner@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6f598f213b729b89650e290c7f62af62fdcb5405..78172f16f62a61da60c4fcf3603e6a535946f6ed 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2113,6 +2113,16 @@ static void shrink_zones(int priority, struct zonelist *zonelist,
                                continue;
                        if (zone->all_unreclaimable && priority != DEF_PRIORITY)
                                continue;       /* Let kswapd poll it */
+                       if (COMPACTION_BUILD) {
+                               /*
+                                * If we already have plenty of memory free
+                                * for compaction, don't free any more.
+                                */
+                               if (sc->order > PAGE_ALLOC_COSTLY_ORDER &&
+                                       (compaction_suitable(zone, sc->order) ||
+                                        compaction_deferred(zone)))
+                                       continue;
+                       }
                        /*
                         * This steals pages from memory cgroups over softlimit
                         * and returns the number of reclaimed pages and