mm: compaction: drop redundant watermark check in compaction_zonelist_suitable()

The watermark check in compaction_zonelist_suitable(), called from
should_compact_retry(), is sandwiched between two watermark checks
already: before, there are freelist attempts as part of direct reclaim and
direct compaction; after, there is a last-minute freelist attempt in
__alloc_pages_may_oom().

The check in compaction_zonelist_suitable() isn't necessary. Kill it.

Link: https://lkml.kernel.org/r/20230519123959.77335-6-hannes@cmpxchg.orgSigned-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/compaction.c

@@ -2278,13 +2278,6 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
 				ac->highest_zoneidx, ac->nodemask) {
 		unsigned long available;
-		unsigned long watermark;
-
-		/* Allocation can already succeed, nothing to do */
-		watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
-		if (zone_watermark_ok(zone, order, watermark,
-				      ac->highest_zoneidx, alloc_flags))
-			continue;
 
 		/*
 		 * Do not consider all the reclaimable memory because we do not