linux-kernel - Re: [PATCH v4 1/4] mm,page_alloc: Bail out earlier on -ENOMEM in alloc_contig_migrate

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Date:   Mon, 15 Mar 2021 12:10:04 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...nel.org>,
        Muchun Song <songmuchun@...edance.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/4] mm,page_alloc: Bail out earlier on -ENOMEM in
 alloc_contig_migrate_range

On 10.03.21 16:08, 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.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>   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 3e4b29ee2b1e..94467f1b85ff 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8484,7 +8484,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
>   			}
>   			tries = 0;
>   		} else if (++tries == 5) {
> -			ret = ret < 0 ? ret : -EBUSY;
> +			ret = -EBUSY;
>   			break;
>   		}
>   
> @@ -8494,6 +8494,12 @@ 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;

I would have thought we could also be able to get other fatal errors 
from migrate_pages(), but doesn't seem like it

Reviewed-by: David Hildenbrand <david@...hat.com>


-- 
Thanks,

David / dhildenb