2021-04-13 14:32:45

by Oscar Salvador

Subject: [PATCH v7 1/7] 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 <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Acked-by: Michal Hocko <[email protected]>
---
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

2021-04-13 21:58:21

by Mike Kravetz

Subject: Re: [PATCH v7 1/7] mm,page_alloc: Bail out earlier on -ENOMEM in alloc_contig_migrate_range

On 4/13/21 3:47 AM, Oscar Salvador wrote:
> 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 <[email protected]>
> Acked-by: Vlastimil Babka <[email protected]>
> Reviewed-by: David Hildenbrand <[email protected]>
> Acked-by: Michal Hocko <[email protected]>

Acked-by: Mike Kravetz <[email protected]>

--
Mike Kravetz