linux-kernel - [PATCH v6 1/5] mm,page_alloc: Bail out earlier on -ENOMEM in alloc_contig_migrate

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Message-Id: <20210319132004.4341-2-osalvador@suse.de>
Date:   Fri, 19 Mar 2021 14:20:00 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Muchun Song <songmuchun@...edance.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>
Subject: [PATCH v6 1/5] mm,page_alloc: Bail out earlier on -ENOMEM in alloc_contig_migrate_range

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@...e.de>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Reviewed-by: David Hildenbrand <david@...hat.com>
Acked-by: Michal Hocko <mhocko@...e.com>
---
 mm/page_alloc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cfc72873961d..a4f67063b85f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8481,7 +8481,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
 			}
 			tries = 0;
 		} else if (++tries == 5) {
-			ret = ret < 0 ? ret : -EBUSY;
+			ret = -EBUSY;
 			break;
 		}
 
@@ -8491,6 +8491,12 @@ 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;
 	}
 	if (ret < 0) {
 		putback_movable_pages(&cc->migratepages);
-- 
2.16.3