[PATCH v9 1/7] mm,page_alloc: Bail out earlier on -ENOMEM in alloc_contig_migrate_range

From: Oscar Salvador
Date: Fri Apr 16 2021 - 03:00:38 EST


Currently, __alloc_contig_migrate_range can generate -EINTR, -ENOMEM or -EBUSY,
and report them down the chain.
The problem is that when migrate_pages() reports -ENOMEM, we keep going till we
exhaust all the try-attempts (5 at the moment) instead of bailing out.

migrate_pages() bails out right away on -ENOMEM because it is considered a fatal
error. Do the same here instead of keep going and retrying.
Note that this is not fixing a real issue, just a cosmetic change. Although we
can save some cycles by backing off ealier

Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
mm/page_alloc.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1c67c99603a3..689454692de1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8697,7 +8697,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
}
tries = 0;
} else if (++tries == 5) {
- ret = ret < 0 ? ret : -EBUSY;
+ ret = -EBUSY;
break;
}

@@ -8707,6 +8707,13 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,

ret = migrate_pages(&cc->migratepages, alloc_migration_target,
NULL, (unsigned long)&mtc, cc->mode, MR_CONTIG_RANGE);
+
+ /*
+ * On -ENOMEM, migrate_pages() bails out right away. It is pointless
+ * to retry again over this error, so do the same here.
+ */
+ if (ret == -ENOMEM)
+ break;
}

lru_cache_enable();
--
2.16.3