From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id EFCC66B01B8 for ; Sun, 13 Jun 2010 14:31:55 -0400 (EDT) Received: from d01relay05.pok.ibm.com (d01relay05.pok.ibm.com [9.56.227.237]) by e2.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id o5DIJAgu014456 for ; Sun, 13 Jun 2010 14:19:10 -0400 Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay05.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o5DIVmLf134896 for ; Sun, 13 Jun 2010 14:31:48 -0400 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id o5DIVlhZ021002 for ; Sun, 13 Jun 2010 15:31:48 -0300 Date: Mon, 14 Jun 2010 00:01:45 +0530 From: Balbir Singh Subject: Re: [RFC][PATCH 1/2] Linux/Guest unmapped page cache control Message-ID: <20100613183145.GM5191@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20100608155140.3749.74418.sendpatchset@L34Z31A.ibm.com> <20100608155146.3749.67837.sendpatchset@L34Z31A.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20100608155146.3749.67837.sendpatchset@L34Z31A.ibm.com> Sender: owner-linux-mm@kvack.org To: kvm Cc: Avi Kivity , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: * Balbir Singh [2010-06-08 21:21:46]: > Selectively control Unmapped Page Cache (nospam version) > > From: Balbir Singh > > This patch implements unmapped page cache control via preferred > page cache reclaim. The current patch hooks into kswapd and reclaims > page cache if the user has requested for unmapped page control. > This is useful in the following scenario > > - In a virtualized environment with cache=writethrough, we see > double caching - (one in the host and one in the guest). As > we try to scale guests, cache usage across the system grows. > The goal of this patch is to reclaim page cache when Linux is running > as a guest and get the host to hold the page cache and manage it. > There might be temporary duplication, but in the long run, memory > in the guests would be used for mapped pages. > - The option is controlled via a boot option and the administrator > can selectively turn it on, on a need to use basis. > > A lot of the code is borrowed from zone_reclaim_mode logic for > __zone_reclaim(). One might argue that the with ballooning and > KSM this feature is not very useful, but even with ballooning, > we need extra logic to balloon multiple VM machines and it is hard > to figure out the correct amount of memory to balloon. With these > patches applied, each guest has a sufficient amount of free memory > available, that can be easily seen and reclaimed by the balloon driver. > The additional memory in the guest can be reused for additional > applications or used to start additional guests/balance memory in > the host. > > KSM currently does not de-duplicate host and guest page cache. The goal > of this patch is to help automatically balance unmapped page cache when > instructed to do so. > > There are some magic numbers in use in the code, UNMAPPED_PAGE_RATIO > and the number of pages to reclaim when unmapped_page_control argument > is supplied. These numbers were chosen to avoid aggressiveness in > reaping page cache ever so frequently, at the same time providing control. > > The sysctl for min_unmapped_ratio provides further control from > within the guest on the amount of unmapped pages to reclaim. > Are there any major objections to this patch? -- 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