From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 044FA6B01AF for ; Mon, 14 Jun 2010 03:04:58 -0400 (EDT) Received: from m2.gw.fujitsu.co.jp ([10.0.50.72]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o5E74tee029659 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Mon, 14 Jun 2010 16:04:55 +0900 Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 6CEA745DE55 for ; Mon, 14 Jun 2010 16:04:54 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 1BA4145DE4F for ; Mon, 14 Jun 2010 16:04:54 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id BFE9AE0800D for ; Mon, 14 Jun 2010 16:04:53 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.249.87.104]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 7B3ADE08001 for ; Mon, 14 Jun 2010 16:04:50 +0900 (JST) Date: Mon, 14 Jun 2010 16:00:21 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [RFC][PATCH 1/2] Linux/Guest unmapped page cache control Message-Id: <20100614160021.7febbdb2.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100614064955.GR5191@balbir.in.ibm.com> References: <20100608155140.3749.74418.sendpatchset@L34Z31A.ibm.com> <20100608155146.3749.67837.sendpatchset@L34Z31A.ibm.com> <20100613183145.GM5191@balbir.in.ibm.com> <20100614092819.cb7515a5.kamezawa.hiroyu@jp.fujitsu.com> <20100614064955.GR5191@balbir.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: balbir@linux.vnet.ibm.com Cc: kvm , Avi Kivity , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Mon, 14 Jun 2010 12:19:55 +0530 Balbir Singh wrote: > > - Why don't you believe LRU ? And if LRU doesn't work well, should it be > > fixed by a knob rather than generic approach ? > > - No side effects ? > > I believe in LRU, just that the problem I am trying to solve is of > using double the memory for caching the same data (consider kvm > running in cache=writethrough or writeback mode, both the hypervisor > and the guest OS maintain a page cache of the same data). As the VM's > grow the overhead is substantial. In my runs I found upto 60% > duplication in some cases. > > > - Linux vm guys tend to say, "free memory is bad memory". ok, for what > free memory created by your patch is used ? IOW, I can't see the benefit. > If free memory that your patch created will be used for another page-cache, > it will be dropped soon by your patch itself. > > Free memory is good for cases when you want to do more in the same > system. I agree that in a bare metail environment that might be > partially true. I don't have a problem with frequently used data being > cached, but I am targetting a consolidated environment at the moment. > Moreover, the administrator has control via a boot option, so it is > non-instrusive in many ways. It sounds that what you want is to improve performance etc. but to make it easy sizing the system and to help admins. Right ? >>From performance perspective, I don't see any advantage to drop caches which can be dropped easily. I just use cpus for the purpose it may no be necessary. Thanks, -Kame -- 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