From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933375Ab1KBQNh (ORCPT ); Wed, 2 Nov 2011 12:13:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38598 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932955Ab1KBQNg (ORCPT ); Wed, 2 Nov 2011 12:13:36 -0400 Message-ID: <4EB16C17.40906@redhat.com> Date: Wed, 02 Nov 2011 18:13:11 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:7.0) Gecko/20110927 Thunderbird/7.0 MIME-Version: 1.0 To: Andrea Arcangeli CC: James Bottomley , Dan Magenheimer , Pekka Enberg , Cyclonus J , Sasha Levin , Christoph Hellwig , David Rientjes , Linus Torvalds , linux-mm@kvack.org, LKML , Andrew Morton , Konrad Wilk , Jeremy Fitzhardinge , Seth Jennings , ngupta@vflare.org, Chris Mason , JBeulich@novell.com, Dave Hansen , Jonathan Corbet Subject: Re: [GIT PULL] mm: frontswap (for 3.2 window) References: <75efb251-7a5e-4aca-91e2-f85627090363@default> <20111027215243.GA31644@infradead.org> <1319785956.3235.7.camel@lappy> <552d2067-474d-4aef-a9a4-89e5fd8ef84f@default> <20111031181651.GF3466@redhat.com> <1320142590.7701.64.camel@dabdike> <4EB16572.70209@redhat.com> <20111102160201.GB18879@redhat.com> In-Reply-To: <20111102160201.GB18879@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/02/2011 06:02 PM, Andrea Arcangeli wrote: > Hi Avi, > > On Wed, Nov 02, 2011 at 05:44:50PM +0200, Avi Kivity wrote: > > If you look at cleancache, then it addresses this concern - it extends > > pagecache through host memory. When dropping a page from the tail of > > the LRU it first goes into tmem, and when reading in a page from disk > > you first try to read it from tmem. However in many workloads, > > cleancache is actually detrimental. If you have a lot of cache misses, > > then every one of them causes a pointless vmexit; considering that > > servers today can chew hundreds of megabytes per second, this adds up. > > On the other side, if you have a use-once workload, then every page that > > falls of the tail of the LRU causes a vmexit and a pointless page copy. > > I also think it's bad design for Virt usage, but hey, without this > they can't even run with cache=writeback/writethrough and they're > forced to cache=off, and then they claim specvirt is marketing, so for > Xen it's better than nothing I guess. Surely Xen can use the pagecache, it uses Linux for I/O just like kvm. > I'm trying right now to evaluate it as a pure zcache host side > optimization. zcache style usage is fine. It's purely internal so no ABI constraints, and no hypercalls either. It's still synchronous though so RAMster like approaches will not work well. -- error compiling committee.c: too many arguments to function