linux-kernel - Re: [PATCH 05/10] mm: vmscan: Do not allow kswapd to scan at maximum priority

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <514A604E.40303@redhat.com>
Date:	Wed, 20 Mar 2013 21:20:14 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Linux-MM <linux-mm@...ck.org>, Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Zlatko Calusic <zcalusic@...sync.net>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	Michal Hocko <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 05/10] mm: vmscan: Do not allow kswapd to scan at maximum
 priority

On 03/17/2013 09:04 AM, Mel Gorman wrote:
> Page reclaim at priority 0 will scan the entire LRU as priority 0 is
> considered to be a near OOM condition. Kswapd can reach priority 0 quite
> easily if it is encountering a large number of pages it cannot reclaim
> such as pages under writeback. When this happens, kswapd reclaims very
> aggressively even though there may be no real risk of allocation failure
> or OOM.
>
> This patch prevents kswapd reaching priority 0 and trying to reclaim
> the world. Direct reclaimers will still reach priority 0 in the event
> of an OOM situation.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
>   mm/vmscan.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7513bd1..af3bb6f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2891,7 +2891,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>   		 */
>   		if (raise_priority || !this_reclaimed)
>   			sc.priority--;
> -	} while (sc.priority >= 0 &&
> +	} while (sc.priority >= 1 &&
>   		 !pgdat_balanced(pgdat, order, *classzone_idx));
>
>   out:
>

If priority 0 is way way way way way too aggressive, what makes
priority 1 safe?

This makes me wonder, are the priorities useful at all to kswapd?

-- 
All rights reversed
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/