From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id B98E76B004A for ; Tue, 30 Nov 2010 21:13:59 -0500 (EST) Subject: Re: [PATCH 1/3] mm: kswapd: Stop high-order balancing when any suitable zone is balanced From: Shaohua Li In-Reply-To: <1291137339-6323-2-git-send-email-mel@csn.ul.ie> References: <1291137339-6323-1-git-send-email-mel@csn.ul.ie> <1291137339-6323-2-git-send-email-mel@csn.ul.ie> Content-Type: text/plain; charset="UTF-8" Date: Wed, 01 Dec 2010 10:13:56 +0800 Message-ID: <1291169636.12777.43.camel@sli10-conroe> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Simon Kirby , KOSAKI Motohiro , Dave Hansen , linux-mm , linux-kernel List-ID: On Wed, 2010-12-01 at 01:15 +0800, Mel Gorman wrote: > When the allocator enters its slow path, kswapd is woken up to balance the > node. It continues working until all zones within the node are balanced. For > order-0 allocations, this makes perfect sense but for higher orders it can > have unintended side-effects. If the zone sizes are imbalanced, kswapd > may reclaim heavily on a smaller zone discarding an excessive number of > pages. The user-visible behaviour is that kswapd is awake and reclaiming > even though plenty of pages are free from a suitable zone. > > This patch alters the "balance" logic to stop kswapd if any suitable zone > becomes balanced to reduce the number of pages it reclaims from other zones. from my understanding, the patch will break reclaim high zone if a low zone meets the high order allocation, even the high zone doesn't meet the high order allocation. This, for example, will make a high order allocation from a high zone fallback to low zone and quickly exhaust low zone, for example DMA. This will break some drivers. -- 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 policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org