From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 20472900117 for ; Sat, 25 Jun 2011 17:33:56 -0400 (EDT) Message-ID: <4E065433.3020502@redhat.com> Date: Sat, 25 Jun 2011 17:33:39 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 1/4] mm: vmscan: Correct check for kswapd sleeping in sleeping_prematurely References: <1308926697-22475-1-git-send-email-mgorman@suse.de> <1308926697-22475-2-git-send-email-mgorman@suse.de> In-Reply-To: <1308926697-22475-2-git-send-email-mgorman@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , =?UTF-8?B?UMOhZHJhaWcgQnJh?= =?UTF-8?B?ZHk=?= , James Bottomley , Colin King , Minchan Kim , Andrew Lutomirski , Johannes Weiner , linux-mm , linux-kernel On 06/24/2011 10:44 AM, Mel Gorman wrote: > During allocator-intensive workloads, kswapd will be woken frequently > causing free memory to oscillate between the high and min watermark. > This is expected behaviour. > > A problem occurs if the highest zone is small. balance_pgdat() > only considers unreclaimable zones when priority is DEF_PRIORITY > but sleeping_prematurely considers all zones. It's possible for this > sequence to occur > > 1. kswapd wakes up and enters balance_pgdat() > 2. At DEF_PRIORITY, marks highest zone unreclaimable > 3. At DEF_PRIORITY-1, ignores highest zone setting end_zone > 4. At DEF_PRIORITY-1, calls shrink_slab freeing memory from > highest zone, clearing all_unreclaimable. Highest zone > is still unbalanced > 5. kswapd returns and calls sleeping_prematurely > 6. sleeping_prematurely looks at *all* zones, not just the ones > being considered by balance_pgdat. The highest small zone > has all_unreclaimable cleared but but the zone is not > balanced. all_zones_ok is false so kswapd stays awake > > This patch corrects the behaviour of sleeping_prematurely to check > the zones balance_pgdat() checked. > > Reported-and-tested-by: PA!draig Brady > Signed-off-by: Mel Gorman 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org