From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 8A1EA6008E4 for ; Mon, 2 Aug 2010 23:48:53 -0400 (EDT) Received: from m1.gw.fujitsu.co.jp ([10.0.50.71]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o733rNRQ022370 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Tue, 3 Aug 2010 12:53:23 +0900 Received: from smail (m1 [127.0.0.1]) by outgoing.m1.gw.fujitsu.co.jp (Postfix) with ESMTP id E410645DE4D for ; Tue, 3 Aug 2010 12:53:22 +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 BD47C45DE50 for ; Tue, 3 Aug 2010 12:53:22 +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 98C501DB8053 for ; Tue, 3 Aug 2010 12:53:22 +0900 (JST) Received: from ml13.s.css.fujitsu.com (ml13.s.css.fujitsu.com [10.249.87.103]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id 424371DB8055 for ; Tue, 3 Aug 2010 12:53:22 +0900 (JST) Date: Tue, 3 Aug 2010 12:48:31 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH -mm 2/5] use ID in page cgroup Message-Id: <20100803124831.8cd5976f.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100803034513.GF3863@balbir.in.ibm.com> References: <20100802191113.05c982e4.kamezawa.hiroyu@jp.fujitsu.com> <20100802191410.cbf03d67.kamezawa.hiroyu@jp.fujitsu.com> <20100803034513.GF3863@balbir.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: balbir@linux.vnet.ibm.com Cc: linux-mm@kvack.org, "nishimura@mxp.nes.nec.co.jp" , vgoyal@redhat.com, m-ikeda@ds.jp.nec.com, gthelen@google.com, "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" List-ID: On Tue, 3 Aug 2010 09:15:13 +0530 Balbir Singh wrote: > * KAMEZAWA Hiroyuki [2010-08-02 19:14:10]: > > > From: KAMEZAWA Hiroyuki > > > > Now, addresses of memory cgroup can be calculated by their ID without complex. > > This patch relplaces pc->mem_cgroup from a pointer to a unsigned short. > > On 64bit architecture, this offers us more 6bytes room per page_cgroup. > > Use 2bytes for blkio-cgroup's page tracking. More 4bytes will be used for > > some light-weight concurrent access. > > > > We may able to move this id onto flags field but ...go step by step. > > > > Changelog: 20100730 > > - fixed some garbage added by debug code in early stage > > > > Signed-off-by: KAMEZAWA Hiroyuki > > --- > > include/linux/page_cgroup.h | 3 ++- > > mm/memcontrol.c | 32 +++++++++++++++++++------------- > > mm/page_cgroup.c | 2 +- > > 3 files changed, 22 insertions(+), 15 deletions(-) > > > > Index: mmotm-0727/include/linux/page_cgroup.h > > =================================================================== > > --- mmotm-0727.orig/include/linux/page_cgroup.h > > +++ mmotm-0727/include/linux/page_cgroup.h > > @@ -12,7 +12,8 @@ > > */ > > struct page_cgroup { > > unsigned long flags; > > - struct mem_cgroup *mem_cgroup; > > + unsigned short mem_cgroup; /* ID of assigned memory cgroup */ > > + unsigned short blk_cgroup; /* Not Used..but will be. */ > > struct page *page; > > struct list_head lru; /* per cgroup LRU list */ > > }; > > Can I recommend that on 64 bit systems, we merge the flag, mem_cgroup > and blk_cgroup into one 8 byte value. We could use > __attribute("packed") and do something like this > It's a next step. > struct page_cgroup { > unsigned int flags; > unsigned short mem_cgroup; > unsigned short blk_cgroup; > ... > } __attribute(("packed")); > > Then we need to make sure we don't use more that 32 bits for flags, > which is very much under control at the moment. > set_bit() requires "long" as its argument. more some trick is required. And, IIUC, packing implies pc->mem_cgroup = mem_cgroup_id; or pc->blk_cgroup = blk_cgroup_id; will have race with set/clear_bit(BIT_XXXX, &pc->flags) This "packing" is not very easy. we have to consider all possible combinations of operations. > This will save us 8 bytes in total on 64 bit systems and nothing on 32 > bit systems, but will enable blkio cgroup to co-exist. > yes. But I have cocnerns of race condition. to do that, we need patch 3-5. (But patch 5 adds spinlock, then no 8bytes reduce.) Let me go step by step. I'm _really_ afraid of race conditions. 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