From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id BCCB46B024D for ; Thu, 22 Jul 2010 02:09:33 -0400 (EDT) Received: from m5.gw.fujitsu.co.jp ([10.0.50.75]) by fgwmail7.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o6M69VqK013541 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Thu, 22 Jul 2010 15:09:31 +0900 Received: from smail (m5 [127.0.0.1]) by outgoing.m5.gw.fujitsu.co.jp (Postfix) with ESMTP id A84B245DE4F for ; Thu, 22 Jul 2010 15:09:30 +0900 (JST) Received: from s5.gw.fujitsu.co.jp (s5.gw.fujitsu.co.jp [10.0.50.95]) by m5.gw.fujitsu.co.jp (Postfix) with ESMTP id 677CC45DE51 for ; Thu, 22 Jul 2010 15:09:30 +0900 (JST) Received: from s5.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s5.gw.fujitsu.co.jp (Postfix) with ESMTP id 3D4FB1DB8063 for ; Thu, 22 Jul 2010 15:09:30 +0900 (JST) Received: from m106.s.css.fujitsu.com (m106.s.css.fujitsu.com [10.249.87.106]) by s5.gw.fujitsu.co.jp (Postfix) with ESMTP id B9C391DB803F for ; Thu, 22 Jul 2010 15:09:29 +0900 (JST) Date: Thu, 22 Jul 2010 15:04:45 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [RFC][PATCH 1/2][memcg] moving memcg's node info array to virtually contiguous array Message-Id: <20100722150445.19a4a701.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100722144356.b9681621.nishimura@mxp.nes.nec.co.jp> References: <20100721195831.6aa8dca5.kamezawa.hiroyu@jp.fujitsu.com> <20100722144356.b9681621.nishimura@mxp.nes.nec.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Daisuke Nishimura Cc: "linux-mm@kvack.org" , "balbir@linux.vnet.ibm.com" , "linux-kernel@vger.kernel.org" List-ID: On Thu, 22 Jul 2010 14:43:56 +0900 Daisuke Nishimura wrote: > On Wed, 21 Jul 2010 19:58:31 +0900 > KAMEZAWA Hiroyuki wrote: > > > These are just a _toy_ level patches yet. My final purpose is to use indexed array > > for mem_cgroup itself, it has IDs. > > > > Background: > > memory cgroup uses struct page_cgroup for tracking all used pages. It's defined as > > == > > struct page_cgroup { > > unsigned long flags; > > struct mem_cgroup *mem_cgroup; > > struct page *page; > > struct list_head lru; /* per cgroup LRU list */ > > }; > > == > > and this increase the cost of per-page-objects dramatically. Now, we have > > troubles on this object. > > 1. Recently, a blkio-tracking guy wants to add "blockio-cgroup" information > > to page_cgroup. But our concern is extra 8bytes per page. > > 2. At tracking dirty page status etc...we need some trick for safe access > > to page_cgroup and memcgroup's information. For example, a small seqlock. > > > > Now, each memory cgroup has its own ID (0-65535). So, if we can replace > > 8byte of pointer "pc->mem_cgroup" with an ID, which is 2 bytes, we may able > > to have another room. (Moreover, I think we can reduce the number of IDs...) > > > > This patch is a trial for implement a virually-indexed on-demand array and > > an example of usage. Any commetns are welcome. > > Hi, > So, your purpose is to: > > - make the size of mem_croup small(by [2/2]) It's just an example to test virt-array. I don't convice it can save memory or make something fast. and I found a bug in free routine.) > - manage all the mem_cgroup in virt-array indexed by its ID(it would be faster > than using css_lookup) yes. > - replace pc->mem_cgroup by its ID and make the size of page_cgroup small > yes. Final style I'm thinking is struct page_cgroup { unsigned long flags; spinlock_t lock; # for lock_page_cgroup() unsigned short memcg; unsigned short blkio; struct page *page; struct list_head list; }; This will be benefical in 64bit. About 32bit, I may have to merge some fields. Or I may have to add some "version" field for updating memcg's statistics without locks. memcg field may be able to be moved onto high-bits of "flags" because it's stable value unless it's not under move_charge. (IIUC, at move_charge, memcg is off-LRU and there are no race with AcctLRU bit v.s. pc->mem_cgroup field. With other flags, lock_page_cgroup() works enough.) Anyway, race with move_charge() will be the last enemy for us to track dirty pages etc...at least, this kind of "make room" job is required, I feel. There are many things to be considered, but I'm a bit in hurry. I'd like to do some preparation before Mel at el rewrites memory-reclaim+writeback complelety. 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