From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752545AbZH1PVw (ORCPT ); Fri, 28 Aug 2009 11:21:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752472AbZH1PVv (ORCPT ); Fri, 28 Aug 2009 11:21:51 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:54309 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752415AbZH1PVu (ORCPT ); Fri, 28 Aug 2009 11:21:50 -0400 Message-ID: In-Reply-To: <20090828151011.GS4889@balbir.in.ibm.com> References: <20090828132015.10a42e40.kamezawa.hiroyu@jp.fujitsu.com> <20090828132438.b33828bc.kamezawa.hiroyu@jp.fujitsu.com> <20090828151011.GS4889@balbir.in.ibm.com> Date: Sat, 29 Aug 2009 00:21:50 +0900 (JST) Subject: Re: [RFC][PATCH 2/5] memcg: uncharge in batched manner From: "KAMEZAWA Hiroyuki" To: balbir@linux.vnet.ibm.com Cc: "KAMEZAWA Hiroyuki" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "nishimura@mxp.nes.nec.co.jp" User-Agent: SquirrelMail/1.4.16 MIME-Version: 1.0 Content-Type: text/plain;charset=iso-2022-jp Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) Importance: Normal Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Balbir Singh さんは書きました： > * KAMEZAWA Hiroyuki [2009-08-28 > 13:24:38]: > >> >> In massive parallel enviroment, res_counter can be a performance >> bottleneck. >> This patch is a trial for reducing lock contention. >> One strong techinque to reduce lock contention is reducing calls by >> batching some amount of calls int one. >> >> Considering charge/uncharge chatacteristic, >> - charge is done one by one via demand-paging. >> - uncharge is done by >> - in chunk at munmap, truncate, exit, execve... >> - one by one via vmscan/paging. >> >> It seems we hace a chance to batched-uncharge. >> This patch is a base patch for batched uncharge. For avoiding >> scattering memcg's structure, this patch adds memcg batch uncharge >> information to the task. please see start/end usage in next patch. >> > > Overall it is a very good idea, can't we do the uncharge at the poin > tof unmap_vmas, exit_mmap, etc so that we don't have to keep > additional data structures around. > We can't. We uncharge when page->mapcount goes down to 0. This is unknown until page_remove_rmap() decrement page->mapcount by "atomic" ops. My first version allocated memcg_batch_info on stack ...and.. I had to pass an extra argument to page_remove_rmap() etc.... That was very ugly ;( Now, I adds per-task memcg_batch_info to task struct. Because it will be always used at exit() and make exit() path much faster, it's not very costly. Thanks, -Kame