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 968DA6B02C6 for ; Thu, 19 Aug 2010 15:03:34 -0400 (EDT) Date: Thu, 19 Aug 2010 14:03:42 -0500 (CDT) From: Christoph Lameter Subject: Re: Over-eager swapping In-Reply-To: <20100819102055.GK2370@arachsys.com> Message-ID: References: <20100804032400.GA14141@localhost> <20100804095811.GC2326@arachsys.com> <20100804114933.GA13527@localhost> <20100804120430.GB23551@arachsys.com> <20100818143801.GA9086@localhost> <20100818144655.GX2370@arachsys.com> <20100818152103.GA11268@localhost> <1282147034.77481.33.camel@useless.localdomain> <20100818155825.GA2370@arachsys.com> <20100819102055.GK2370@arachsys.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Chris Webb Cc: Lee Schermerhorn , Wu Fengguang , Minchan Kim , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , KOSAKI Motohiro , Pekka Enberg , Andi Kleen List-ID: On Thu, 19 Aug 2010, Chris Webb wrote: > I tried this on a handful of the problem hosts before re-adding their swap. > One of them now runs without dipping into swap. The other three I tried had > the same behaviour of sitting at zero swap usage for a while, before > suddenly spiralling up with %wait going through the roof. I had to swapoff > on them to bring them back into a sane state. So it looks like it helps a > bit, but doesn't cure the problem. > > I could definitely believe an explanation that we're swapping in preference > to allocating remote zone pages somehow, given the imbalance in free memory > between the nodes which we saw. However, I read the documentation for > vm.zone_reclaim_mode, which suggests to me that when it was set to zero, > pages from remote zones should be allocated automatically in preference to > swap given that zone_reclaim_mode & 4 == 0? If zone reclaim is off then pages from other nodes will be allocated if a node is filled up with page cache. zone reclaim typically only evicts clean page cache pages in order to keep the additional overhead down. Enabling swapping allows a more aggressive form of recovering memory in preference of going off line. The VM should work fine even without zone reclaim. -- 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