From: Zi Yan ziy@nvidia.com Subject: mm/compaction: stop isolation if too many pages are isolated and we have pages to migrate

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.

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.

[vbabka@suse.cz: changelog addition] Link: https://lkml.kernel.org/r/20201030183809.3616803-2-zi.yan@sent.com Fixes: 1da2f328fa64 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”) Signed-off-by: Zi Yan ziy@nvidia.com Suggested-by: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Cc: Mel Gorman mgorman@techsingularity.net Cc: Michal Hocko mhocko@kernel.org Cc: Rik van Riel riel@surriel.com Cc: Yang Shi shy828301@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/compaction.c | 4 ++++ 1 file changed, 4 insertions(+)

--- a/mm/compaction.c~mm-compaction-stop-isolation-if-too-many-pages-are-isolated-and-we-have-pages-to-migrate +++ a/mm/compaction.c @@ -817,6 +817,10 @@ isolate_migratepages_block(struct compac * 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; _