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 ESMTP id 8CA606B020A for ; Thu, 19 Aug 2010 11:14:27 -0400 (EDT) Received: from d01relay05.pok.ibm.com (d01relay05.pok.ibm.com [9.56.227.237]) by e7.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id o7JF0cOY003309 for ; Thu, 19 Aug 2010 11:00:38 -0400 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay05.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o7JFELw4123742 for ; Thu, 19 Aug 2010 11:14:21 -0400 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id o7JFEK7p024825 for ; Thu, 19 Aug 2010 11:14:20 -0400 Date: Thu, 19 Aug 2010 20:43:51 +0530 From: Balbir Singh Subject: Re: Over-eager swapping Message-ID: <20100819151351.GA23611@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20100819051339.GH28417@balbir.in.ibm.com> <20100818164539.GG28417@balbir.in.ibm.com> <20100819092536.GH2370@arachsys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20100819092536.GH2370@arachsys.com> Sender: owner-linux-mm@kvack.org To: Chris Webb Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Wu Fengguang , Minchan Kim , KOSAKI Motohiro List-ID: * Chris Webb [2010-08-19 10:25:36]: > Balbir Singh writes: > > > Can you give an idea of what the meminfo inside the guest looks like. > > Sorry for the slow reply here. Unfortunately not, as these guests are run on > behalf of customers. They install them with operating systems of their > choice, and run them on our service. > Thanks for clarifying. > > Have you looked at > > http://kerneltrap.org/mailarchive/linux-kernel/2010/6/8/4580772 > > Yes, I've been watching this discussions with interest. Our application is > one where we have little to no control over what goes on inside the guests, > but these sorts of things definitely make sense where the two are under the > same administrative control. > Not necessarily, in some cases you can use a guest that uses lesser page cache, but that might not matter in your case at the moment. > > Do we have reason to believe the problem can be solved entirely in the > > host? > > It's not clear to me why this should be difficult, given that the total size > of vm allocated to guests (and system processes) is always strictly less > than the total amount of RAM available in the host. I do understand that it > won't allow for as impressive overcommit (except by ksm) or be as efficient, > because file-backed guest pages won't get evicted by pressure in the host as > they are indistinguishable from anonymous pages. > > After all, a solution that isn't ideal, but does work, is to turn off swap > completely! This is what we've been doing to date. The only problem with > this is that we can't dip into swap in an emergency if there's no swap there > at all. If you are not overcommitting it should work, in my experiments I've seen a lot of memory used by the host as page cache on behalf of the guest. I've done my experiments using cgroups to identify accurate usage. -- Three Cheers, Balbir -- 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