From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx103.postini.com [74.125.245.103]) by kanga.kvack.org (Postfix) with SMTP id 15FAD6B0068 for ; Thu, 28 Jun 2012 04:36:12 -0400 (EDT) Received: from m1.gw.fujitsu.co.jp (unknown [10.0.50.71]) by fgwmail6.fujitsu.co.jp (Postfix) with ESMTP id 2CE613EE0B6 for ; Thu, 28 Jun 2012 17:36:11 +0900 (JST) Received: from smail (m1 [127.0.0.1]) by outgoing.m1.gw.fujitsu.co.jp (Postfix) with ESMTP id 0BE3F45DE5C for ; Thu, 28 Jun 2012 17:36:11 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (s1.gw.fujitsu.co.jp [10.0.50.91]) by m1.gw.fujitsu.co.jp (Postfix) with ESMTP id E266845DE55 for ; Thu, 28 Jun 2012 17:36:10 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id D0E461DB8057 for ; Thu, 28 Jun 2012 17:36:10 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.240.81.134]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id 87D271DB804D for ; Thu, 28 Jun 2012 17:36:10 +0900 (JST) Message-ID: <4FEC16EF.40408@jp.fujitsu.com> Date: Thu, 28 Jun 2012 17:33:51 +0900 From: Kamezawa Hiroyuki MIME-Version: 1.0 Subject: Re: [PATCH v3][0/6] memcg: prevent -ENOMEM in pre_destroy() References: <4FACDED0.3020400@jp.fujitsu.com> <20120621202043.GD4642@google.com> <4FE3ADDD.9060908@jp.fujitsu.com> <20120627175818.GM15811@google.com> In-Reply-To: <20120627175818.GM15811@google.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: "linux-mm@kvack.org" , "cgroups@vger.kernel.org" , Michal Hocko , Johannes Weiner , Frederic Weisbecker , Han Ying , Glauber Costa , "Aneesh Kumar K.V" , Andrew Morton , Hiroyuki Kamezawa , Linux Kernel (2012/06/28 2:58), Tejun Heo wrote: > Hello, KAME. > > On Fri, Jun 22, 2012 at 08:27:25AM +0900, Kamezawa Hiroyuki wrote: >> Remaining 20% of work is based on a modification to cgroup layer >> >> How do you think this patch ? (This patch is not tested yet...so >> may have troubles...) I think callers of pre_destory() is not so many... >> >> == >> From a28db946f91f3509d25779e8c5db249506cc4b07 Mon Sep 17 00:00:00 2001 >> From: KAMEZAWA Hiroyuki >> Date: Fri, 22 Jun 2012 08:38:38 +0900 >> Subject: [PATCH] cgroup: keep cgroup_mutex() while calling ->pre_destroy() >> >> In past, memcg's pre_destroy() was verrry slow because of the possibility >> of page reclaiming in it. So, cgroup_mutex() was released before calling >> pre_destroy() callbacks. Now, it's enough fast. memcg just scans the list >> and move pages to other cgroup, no memory reclaim happens. >> Then, we can keep cgroup_mutex() there. >> >> By holding looks, we can avoid following cases >> 1. new task is attached while rmdir(). >> 2. new child cgroup is created while rmdir() >> 3. new task is attached to cgroup and removed from cgroup before >> checking css's count. So, ->destroy() will be called even if >> some trashes by the task remains >> >> (3. is terrible case...even if I think it will not happen in real world..) > > Ooh, once memcg drops the __DEPRECATED_clear_css_refs, cgroup_rmdir() > will mark the cgroup dead before start calling pre_destroy() and none > of the above will happen. > Hm, threads which touches memcg should hold memcg's reference count rather than css. Right ? IIUC, one of reason is a reference from kswapd etc...hm. I'll check it. 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