From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx116.postini.com [74.125.245.116]) by kanga.kvack.org (Postfix) with SMTP id 3F2F46B0002 for ; Thu, 21 Mar 2013 08:30:57 -0400 (EDT) Message-ID: <514AFD71.5080509@redhat.com> Date: Thu, 21 Mar 2013 08:30:41 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 05/10] mm: vmscan: Do not allow kswapd to scan at maximum priority References: <1363525456-10448-1-git-send-email-mgorman@suse.de> <1363525456-10448-6-git-send-email-mgorman@suse.de> <514A604E.40303@redhat.com> <20130321101210.GF1878@suse.de> In-Reply-To: <20130321101210.GF1878@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Linux-MM , Jiri Slaby , Valdis Kletnieks , Zlatko Calusic , Johannes Weiner , dormando , Satoru Moriya , Michal Hocko , LKML On 03/21/2013 06:12 AM, Mel Gorman wrote: > On Wed, Mar 20, 2013 at 09:20:14PM -0400, Rik van Riel wrote: >> 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 >>> --- >>> 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? >> > > The fact that priority 1 selects a sensible number of pages to reclaim and > obeys swappiness makes it a lot safer. Priority 0 does this in get_scan_count ^^^^^^^^^^^^^^^^ Ahhh, good point! We stay away from all the "emergency" code, which kswapd should never run. Acked-by: Rik van Riel -- All rights reversed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org