From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id EBC986B004A for ; Tue, 30 Nov 2010 22:28:54 -0500 (EST) Received: from m1.gw.fujitsu.co.jp ([10.0.50.71]) by fgwmail7.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id oB13Sqen029515 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Wed, 1 Dec 2010 12:28:52 +0900 Received: from smail (m1 [127.0.0.1]) by outgoing.m1.gw.fujitsu.co.jp (Postfix) with ESMTP id E97C145DE54 for ; Wed, 1 Dec 2010 12:28:51 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (s1.gw.fujitsu.co.jp [10.0.50.91]) by m1.gw.fujitsu.co.jp (Postfix) with ESMTP id C845945DE55 for ; Wed, 1 Dec 2010 12:28:51 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id BA362E38002 for ; Wed, 1 Dec 2010 12:28:51 +0900 (JST) Received: from m108.s.css.fujitsu.com (m108.s.css.fujitsu.com [10.249.87.108]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id 792D3E08002 for ; Wed, 1 Dec 2010 12:28:51 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH 1/3] mm: kswapd: Stop high-order balancing when any suitable zone is balanced In-Reply-To: <1291173628.12777.65.camel@sli10-conroe> References: <20101201115401.ABB1.A69D9226@jp.fujitsu.com> <1291173628.12777.65.camel@sli10-conroe> Message-Id: <20101201122638.ABBF.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Date: Wed, 1 Dec 2010 12:28:50 +0900 (JST) Sender: owner-linux-mm@kvack.org To: Shaohua Li Cc: kosaki.motohiro@jp.fujitsu.com, Mel Gorman , Simon Kirby , Dave Hansen , linux-mm , linux-kernel List-ID: > On Wed, 2010-12-01 at 10:59 +0800, KOSAKI Motohiro wrote: > > > On Wed, 2010-12-01 at 10:23 +0800, KOSAKI Motohiro wrote: > > > > > 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. > > > > > > > > Have you seen patch [3/3]? I think it migigate your pointed issue. > > > yes, it improves a lot, but still possible for small systems. > > > > Ok, I got you. so please define your "small systems" word? > an embedded system with less memory memory, obviously Typical embedded system don't have multiple zone. It's not obvious. > > we can't make > > perfect VM heuristics obviously, then we need to compare pros/cons. > if you don't care about small system, let's consider a NORMAL i386 > system with 896m normal zone, and 896M*3 high zone. normal zone will > quickly exhaust by high order high zone allocation, leave a latter > allocation which does need normal zone fail. Not happen. slab don't allocate from highmem and page cache allocation is always using order-0. When happen high order high zone allocation? -- 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