mm: remove reclaim and compaction retry approximations

If per-zone LRU accounting is available then there is no point
approximating whether reclaim and compaction should retry based on pgdat
statistics.  This is effectively a revert of "mm, vmstat: remove zone
and node double accounting by approximating retries" with the difference
that inactive/active stats are still available.  This preserves the
history of why the approximation was retried and why it had to be
reverted to handle OOM kills on 32-bit systems.

Link: http://lkml.kernel.org/r/1469110261-7365-4-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 19 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index cd93ea24c565..e5995f38d677 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1438,11 +1438,6 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 {
         struct zone *zone;
         struct zoneref *z;
-        pg_data_t *last_pgdat = NULL;
-
-        /* Do not retry compaction for zone-constrained allocations */
-        if (ac->high_zoneidx < ZONE_NORMAL)
-                return false;
 
         /*
          * Make sure at least one zone would pass __compaction_suitable if we continue
@@ -1453,27 +1448,14 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
                 unsigned long available;
                 enum compact_result compact_result;
 
-                if (last_pgdat == zone->zone_pgdat)
-                        continue;
-
-                /*
-                 * This over-estimates the number of pages available for
-                 * reclaim/compaction but walking the LRU would take too
-                 * long. The consequences are that compaction may retry
-                 * longer than it should for a zone-constrained allocation
-                 * request.
-                 */
-                last_pgdat = zone->zone_pgdat;
-                available = pgdat_reclaimable_pages(zone->zone_pgdat) / order;
-
                 /*
                  * Do not consider all the reclaimable memory because we do not
                  * want to trash just for a single high order allocation which
                  * is even not guaranteed to appear even if __compaction_suitable
                  * is happy about the watermark check.
                  */
+                available = zone_reclaimable_pages(zone) / order;
                 available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
-                available = min(zone->managed_pages, available);
                 compact_result = __compaction_suitable(zone, order, alloc_flags,
                                 ac_classzone_idx(ac), available);
                 if (compact_result != COMPACT_SKIPPED &&