[PATCH v3] mm/compaction: fix set skip in fast_find_migrateblock

[Chuyi Zhou <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%*

Fixes: 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 962d05d1e187..abc7b0834471 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1850,7 +1850,6 @@ 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