Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751514Ab1CJVQ7 (ORCPT ); Thu, 10 Mar 2011 16:16:59 -0500 Received: from rcsinet10.oracle.com ([148.87.113.121]:62134 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751188Ab1CJVQ5 (ORCPT ); Thu, 10 Mar 2011 16:16:57 -0500 Content-Type: text/plain; charset=UTF-8 From: Chris Mason To: Vivek Goyal Cc: Justin TerAvest , KAMEZAWA Hiroyuki , m-ikeda , jaxboe , linux-kernel , ryov , taka , "righi.andrea" , guijianfeng , balbir , ctalbott , nauman , mrubin , linux-fsdevel Subject: Re: [RFC] Storing cgroup id in page->private (Was: Re: [RFC] [PATCH 0/6] Provide cgroup isolation for buffered writes.) In-reply-to: <20110310194106.GH29464@redhat.com> References: <1299619256-12661-1-git-send-email-teravest@google.com> <20110309142237.6ab82523.kamezawa.hiroyu@jp.fujitsu.com> <20110310181529.GF29464@redhat.com> <20110310191115.GG29464@redhat.com> <20110310194106.GH29464@redhat.com> Date: Thu, 10 Mar 2011 16:15:39 -0500 Message-Id: <1299791640-sup-1874@think> User-Agent: Sup/git Content-Transfer-Encoding: 8bit X-Source-IP: acsmt355.oracle.com [141.146.40.155] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090209.4D793FA9.00D5,ss=1,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3237 Lines: 65 Excerpts from Vivek Goyal's message of 2011-03-10 14:41:06 -0500: > On Thu, Mar 10, 2011 at 02:11:15PM -0500, Vivek Goyal wrote: > > On Thu, Mar 10, 2011 at 10:57:52AM -0800, Justin TerAvest wrote: > > > On Thu, Mar 10, 2011 at 10:15 AM, Vivek Goyal wrote: > > > > On Thu, Mar 10, 2011 at 10:08:03AM -0800, Justin TerAvest wrote: > > > > > > > > [..] > > > >> > I don't like to increase size of page_cgroup but I think you can record > > > >> > information without increasing size of page_cgroup. > > > >> > > > > >> > A) As Andrea did, encode it to pc->flags. > > > >> >   But I'm afraid that there is a racy case because memory cgroup uses some > > > >> >   test_and_set() bits. > > > >> > B) I wonder why the information cannot be recorded in page->private. > > > >> >   When page has buffers, you can record the information to buffer struct. > > > >> >   About swapio (if you take care of), you can record information to bio. > > > >> > > > >> Hi Kame, > > > >> > > > >> I'm concerned that by using something like buffer_heads stored in > > > >> page->private, we will only be supported on some filesystems and not > > > >> others. In addition, I'm not sure if all filesystems attach buffer > > > >> heads at the same time; if page->private is modified in the flusher > > > >> thread, we might not be able to determine the thread that dirtied the > > > >> page in the first place. > > > > > > > > I think the person who dirtied the page can store the information in > > > > page->private (assuming buffer heads were not generated) and if flusher > > > > thread later ends up generating buffer heads and ends up modifying > > > > page->private, this can be copied in buffer heads? > > > > > > This scares me a bit. > > > > > > As I understand it, fs/ code expects total ownership of page->private. > > > This adds a responsibility for every user to copy the data through and > > > store it in the buffer head (or anything else). btrfs seems to do > > > something entirely different in some cases and store a different kind > > > of value. > > > > If filesystems are using page->private for some other purpose also, then > > I guess we have issues. > > > > I am ccing linux-fsdevel to have some feedback on the idea of trying > > to store cgroup id of page dirtying thread in page->private and/or buffer > > head for tracking which group originally dirtied the page in IO controller > > during writeback. > > A quick "grep" showed that btrfs, ceph and logfs are using page->private > for other purposes also. > > I was under the impression that either page->private is null or it > points to buffer heads for the writeback case. So storing the info > directly in either buffer head directly or first in page->private and > then transferring it to buffer heads would have helped. Right, btrfs has its own uses for page->private, and we expect to own it. With a proper callback, the FS could store the extra information you need in out own structs. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/