From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 12 Nov 2008 17:04:00 -0800 From: Andrew Morton Subject: Re: [RFC][PATCH 1/6] memcg: free all at rmdir Message-Id: <20081112170400.bfb7211c.akpm@linux-foundation.org> In-Reply-To: <491B7978.7010300@linux.vnet.ibm.com> References: <20081112122606.76051530.kamezawa.hiroyu@jp.fujitsu.com> <20081112122656.c6e56248.kamezawa.hiroyu@jp.fujitsu.com> <20081112160758.3dca0b22.akpm@linux-foundation.org> <491B7395.8040606@linux.vnet.ibm.com> <20081112164637.b6f3cb78.akpm@linux-foundation.org> <491B7978.7010300@linux.vnet.ibm.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: balbir@linux.vnet.ibm.com Cc: kamezawa.hiroyu@jp.fujitsu.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, nishimura@mxp.nes.nec.co.jp, menage@google.com List-ID: On Thu, 13 Nov 2008 06:18:56 +0530 Balbir Singh wrote: > Andrew Morton wrote: > > On Thu, 13 Nov 2008 05:53:49 +0530 > > Balbir Singh wrote: > > > >> Andrew Morton wrote: > >>> On Wed, 12 Nov 2008 12:26:56 +0900 > >>> KAMEZAWA Hiroyuki wrote: > >>> > >>>> +5.1 on_rmdir > >>>> +set behavior of memcg at rmdir (Removing cgroup) default is "drop". > >>>> + > >>>> +5.1.1 drop > >>>> + #echo on_rmdir drop > memory.attribute > >>>> + This is default. All pages on the memcg will be freed. > >>>> + If pages are locked or too busy, they will be moved up to the parent. > >>>> + Useful when you want to drop (large) page caches used in this memcg. > >>>> + But some of in-use page cache can be dropped by this. > >>>> + > >>>> +5.1.2 keep > >>>> + #echo on_rmdir keep > memory.attribute > >>>> + All pages on the memcg will be moved to its parent. > >>>> + Useful when you don't want to drop page caches used in this memcg. > >>>> + You can keep page caches from some library or DB accessed by this > >>>> + memcg on memory. > >>> Would it not be more useful to implement a per-memcg version of > >>> /proc/sys/vm/drop_caches? (One without drop_caches' locking bug, > >>> hopefully). > >>> > >>> If we do this then we can make the above "keep" behaviour non-optional, > >>> and the operator gets to choose whether or not to drop the caches > >>> before doing the rmdir. > >>> > >>> Plus, we get a new per-memcg drop_caches capability. And it's a nicer > >>> interface, and it doesn't have the obvious races which on_rmdir has, > >>> etc. > >>> > >> Andrew, I suspect that will not be easy, since we don't track address spaces > >> that belong to a particular memcg. If page cache ends up being shared across > >> memcg's, dropping them would impact both mem cgroups. > >> > > > > walk the LRUs? > > We do that for the force_empty() interface we have. Although we don't > differentiate between cache and RSS at the moment. so.. what's wrong with using that (possibly with some generalisation/enhancement)? btw, mem_cgroup_force_empty_list() uses PageLRU() outside ->lru_lock. That's racy, although afaict this race will only cause an accounting error. Or maybe not. What happens if __mem_cgroup_uncharge_common()->__mem_cgroup_remove_list() is passed a page which isn't on an LRU any more? boom? -- 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