mm, page_alloc: wakeup kcompactd even if kswapd cannot free more memory

Kswapd will not wakeup if per-zone watermarks are not failing or if too
many previous attempts at background reclaim have failed.

This can be true if there is a lot of free memory available.  For high-
order allocations, kswapd is responsible for waking up kcompactd for
background compaction.  If the zone is not below its watermarks or
reclaim has recently failed (lots of free memory, nothing left to
reclaim), kcompactd does not get woken up.

When __GFP_DIRECT_RECLAIM is not allowed, allow kcompactd to still be
woken up even if kswapd will not reclaim.  This allows high-order
allocations, such as thp, to still trigger background compaction even
when the zone has an abundance of free memory.

Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1803111659420.209721@chino.kir.corp.google.com
Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 6 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f6005b7c3446..02c1a60d7937 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3805,16 +3805,18 @@ retry:
         return page;
 }
 
-static void wake_all_kswapds(unsigned int order, const struct alloc_context *ac)
+static void wake_all_kswapds(unsigned int order, gfp_t gfp_mask,
+                             const struct alloc_context *ac)
 {
         struct zoneref *z;
         struct zone *zone;
         pg_data_t *last_pgdat = NULL;
+        enum zone_type high_zoneidx = ac->high_zoneidx;
 
-        for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
-                                        ac->high_zoneidx, ac->nodemask) {
+        for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, high_zoneidx,
+                                        ac->nodemask) {
                 if (last_pgdat != zone->zone_pgdat)
-                        wakeup_kswapd(zone, order, ac->high_zoneidx);
+                        wakeup_kswapd(zone, gfp_mask, order, high_zoneidx);
                 last_pgdat = zone->zone_pgdat;
         }
 }
@@ -4093,7 +4095,7 @@ retry_cpuset:
                 goto nopage;
 
         if (gfp_mask & __GFP_KSWAPD_RECLAIM)
-                wake_all_kswapds(order, ac);
+                wake_all_kswapds(order, gfp_mask, ac);
 
         /*
          * The adjusted alloc_flags might result in immediate success, so try
@@ -4151,7 +4153,7 @@ retry_cpuset:
 retry:
         /* Ensure kswapd doesn't accidentally go to sleep as long as we loop */
         if (gfp_mask & __GFP_KSWAPD_RECLAIM)
-                wake_all_kswapds(order, ac);
+                wake_all_kswapds(order, gfp_mask, ac);
 
         reserve_flags = __gfp_pfmemalloc_flags(gfp_mask);
         if (reserve_flags)