[PATCH v2] mm/compaction: fix set skip in fast_find_migrateblock

[Zhou Chuyi <zhouchuyi@bytedance.com>]

From: zhouchuyi <zhouchuyi@bytedance.com>

When we successfully find a pageblock in
fast_find_migrateblock(), the block will be set
skip-flag through set_pageblock_skip().
However, when entering isolate_migratepages_block(),
the whole pageblock will be skipped due to the branch
'if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages))'.
Eventually we will goto isolate_abort and isolate nothing.
That cause fast_find_migrateblock useless.

In this Patch, when we find a suitable pageblock in
fast_find_migrateblock, we do noting but let
isolate_migratepages_block to set skip flag to
the pageblock after scan it. Normally, we would
isolate some pages from the fast-find block.

I use mmtest/thpscale-madvhugepage test it. Here
is the result:
			    baseline		   patch
Amean     fault-both-1      1331.66 (   0.00%)     1261.04 *   5.30%*
Amean     fault-both-3      1383.95 (   0.00%)     1191.69 *  13.89%*
Amean     fault-both-5      1568.13 (   0.00%)     1445.20 *   7.84%*
Amean     fault-both-7      1819.62 (   0.00%)     1555.13 *  14.54%*
Amean     fault-both-12     1106.96 (   0.00%)     1149.43 *  -3.84%*
Amean     fault-both-18     2196.93 (   0.00%)     1875.77 *  14.62%*
Amean     fault-both-24     2642.69 (   0.00%)     2671.21 *  -1.08%*
Amean     fault-both-30     2901.89 (   0.00%)     2857.32 *   1.54%*
Amean     fault-both-32     3747.00 (   0.00%)     3479.23 *   7.15%*

Fixs: 'commit 70b44595eafe9 ("mm, compaction: use free lists
to quickly locate a migration source")'

Signed-off-by: zhouchuyi <zhouchuyi@bytedance.com>
---
 mm/compaction.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 1f89b969c..a1a2b50c8 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1852,7 +1852,6 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
 					pfn = cc->zone->zone_start_pfn;
 				cc->fast_search_fail = 0;
 				found_block = true;
-				set_pageblock_skip(freepage);
 				break;
 			}
 		}
-- 
2.20.1