On 10/30/20 7:38 PM, Zi Yan wrote:
From: Zi Yan <ziy@xxxxxxxxxx>
In isolate_migratepages_block, if we have too many isolated pages and
nr_migratepages is not zero, we should try to migrate what we have
without wasting time on isolating.
As you CC stable, there should be a stronger reason (strictly speaking the
problem should have been observed in practice, but this is a simple patch, so
they could accept it), so I suggest Andrew adds the following paragraph:
In theory it's possible that multiple parallel compactions will cause
too_many_isolated() to become true even if each has isolated less than
COMPACT_CLUSTER_MAX, and loop forever in the while loop. Bailing immediately
prevents that.
Fixes: 1da2f328fa64 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”)
Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
---
mm/compaction.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/compaction.c b/mm/compaction.c
index 3e834ac402f1..4d237a7c3830 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -817,6 +817,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
* delay for some time until fewer pages are isolated
*/
while (unlikely(too_many_isolated(pgdat))) {
+ /* stop isolation if there are still pages not migrated */
+ if (cc->nr_migratepages)
+ return 0;
+
/* async migration should just abort */
if (cc->mode == MIGRATE_ASYNC)
return 0;
