From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751689Ab1KBU1b (ORCPT ); Wed, 2 Nov 2011 16:27:31 -0400 Received: from acsinet15.oracle.com ([141.146.126.227]:59520 "EHLO acsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750920Ab1KBU12 convert rfc822-to-8bit (ORCPT ); Wed, 2 Nov 2011 16:27:28 -0400 MIME-Version: 1.0 Message-ID: <1ef1abbc-f092-4784-9f2e-1d9ca151e9e0@default> Date: Wed, 2 Nov 2011 13:27:01 -0700 (PDT) From: Dan Magenheimer To: Avi Kivity , Andrea Arcangeli Cc: James Bottomley , 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 4EB16C17.40906@redhat.com> In-Reply-To: <4EB16C17.40906@redhat.com> X-Priority: 3 X-Mailer: Oracle Beehive Extensions for Outlook 2.0.1.4.1.0 (410211) [OL 12.0.6562.5003] Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT X-Source-IP: acsinet21.oracle.com [141.146.126.237] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090206.4EB1A79A.006E,ss=1,re=0.000,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: Avi Kivity [mailto:avi@redhat.com] > Subject: Re: [GIT PULL] mm: frontswap (for 3.2 window) > > 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. Still experimental, but only the initial local put must be synchronous. RAMster uses a separate thread to "remotify" pre-compressed pages. The "get" still needs to be synchronous, but (if I ever have time to get back to coding it) I've got some ideas on how to fix that. If I manage to get that working, perhaps it could be used for Andrea's write-precompressed-zcache-pages-to-disk. Dan