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From: Zi Yan <zi.yan@sent.com>
To: Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org
Cc: Rik van Riel <riel@surriel.com>,
	linux-kernel@vger.kernel.org, Zi Yan <ziy@nvidia.com>
Subject: [PATCH] mm/compaction: count pages and stop correctly during page isolation.
Date: Thu, 29 Oct 2020 16:04:35 -0400
Message-ID: <20201029200435.3386066-1-zi.yan@sent.com> (raw)

From: Zi Yan <ziy@nvidia.com>

In isolate_migratepages_block, when cc->alloc_contig is true, we are
able to isolate compound pages, nr_migratepages and nr_isolated did not
count compound pages correctly, causing us to isolate more pages than we
thought. Use thp_nr_pages to count pages. Otherwise, we might be trapped
in too_many_isolated while loop, since the actual isolated pages can go
up to COMPACT_CLUSTER_MAX*512=16384, where COMPACT_CLUSTER_MAX is 32,
since we stop isolation after cc->nr_migratepages reaches to
COMPACT_CLUSTER_MAX.

In addition, after we fix the issue above, cc->nr_migratepages could
never be equal to COMPACT_CLUSTER_MAX if compound pages are isolated,
thus page isolation could not stop as we intended. Change the isolation
stop condition to >=.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/compaction.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index ee1f8439369e..0683a4999581 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1012,8 +1012,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 
 isolate_success:
 		list_add(&page->lru, &cc->migratepages);
-		cc->nr_migratepages++;
-		nr_isolated++;
+		cc->nr_migratepages += thp_nr_pages(page);
+		nr_isolated += thp_nr_pages(page);
 
 		/*
 		 * Avoid isolating too much unless this block is being
@@ -1021,7 +1021,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		 * or a lock is contended. For contention, isolate quickly to
 		 * potentially remove one source of contention.
 		 */
-		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX &&
+		if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
 		    !cc->rescan && !cc->contended) {
 			++low_pfn;
 			break;
@@ -1132,7 +1132,7 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
 		if (!pfn)
 			break;
 
-		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
+		if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
 			break;
 	}
 
-- 
2.28.0



             reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-29 20:04 Zi Yan [this message]
2020-10-29 21:14 ` Yang Shi
2020-10-29 21:31   ` Zi Yan
2020-10-30  0:28     ` Andrew Morton
2020-10-30  1:20       ` Zi Yan
2020-10-30  9:43 ` Michal Hocko
2020-10-30 12:20   ` Zi Yan
2020-10-30 13:36     ` Michal Hocko
2020-10-30 14:35       ` Zi Yan
2020-10-30 14:49         ` Michal Hocko
2020-10-30 14:53           ` Zi Yan
2020-10-30 14:55           ` Vlastimil Babka
2020-10-30 18:33       ` Yang Shi
2020-10-30 18:39         ` Zi Yan
2020-10-30 18:55           ` Yang Shi
2020-11-02 13:03             ` Vlastimil Babka
2020-11-02 16:39               ` Yang Shi
2020-10-30 14:50 ` Vlastimil Babka
2020-10-30 15:18   ` Zi Yan

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