From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 23 May 2008 12:10:27 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH 0/4] swapcgroup(v2) Message-Id: <20080523121027.b0eecfa0.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20080522222655.166657da@bree.surriel.com> References: <48350F15.9070007@mxp.nes.nec.co.jp> <20080522222655.166657da@bree.surriel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Rik van Riel Cc: Daisuke Nishimura , Linux Containers , Linux MM , Balbir Singh , Pavel Emelyanov , YAMAMOTO Takashi , Hugh Dickins , "IKEDA, Munehiro" List-ID: On Thu, 22 May 2008 22:26:55 -0400 Rik van Riel wrote: > Even worse is that a cgroup has NO CONTROL over how much > of its memory is kept in RAM and how much is swapped out. Could you explain "NO CONTROL" ? cgroup has LRU.... 'how mucch memory should be swapped out from memory' is well controlled in the VM besides LRU logic ? > This kind of decision is made on a system-wide basis by > the kernel, dependent on what other processes in the system > are doing. There also is no easy way for a cgroup to reduce > its swap use, unlike with other resources. > > In what scenario would you use a resource controller that > rewards a group for reaching its limit? > > How can the cgroup swap space controller help sysadmins > achieve performance or fairness goals on a system? > Perforamnce is not the first goal of this swap controller, I think. This is for resouce isolation/overcommiting. 1. Some _crazy_ people considers swap as very-slow-memory resource ;) I don't think so but I know there are tons of people.... 2. Resource Isolation. When a cgroup has memory limitation, it can create tons of swap. For example, limit a cgroup's memory to be 128M and malloc 3G bytes. 2.8Gbytes of swap will be used _easily_. A process can use up all swap. In that case, other process can't use swap. IIRC, a man shown his motivation to controll swap in OLS2007/BOF as following. == Consider following system. (and there is no swap controller.) Memory 4G. Swap 1G. with 2 cgroups A, B. state 1) swap is not used. A....memory limit to be 1G no swap usage memory_usage=0M B....memory limit to be 1G no swap usage memory_usage=0M state 2) Run a big program on A. A....memory limit to be 1G and try to use 1.7G. uses 700MBytes of swap. memory_usage=1G swap_usage=700M B....memory_usage=0M state 3) A some of programs ends in 'A' A....memory_usage=500M swap_usage=700M B....memory_usage=0M. state 4) Run a big program on B. A...memory_usage=500M swap_usage=700M. B...memory_usage=1G swap_usage=300M Group B can only use 1.3G because of unfair swap use of group A. But users think why A uses 700M of swap with 500M of free memory.... If we don't have limitation to swap, we'll have to innovate a way to move swap to memory in some reasonable logic. 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