Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754380Ab2FSObi (ORCPT ); Tue, 19 Jun 2012 10:31:38 -0400 Received: from mail-yx0-f174.google.com ([209.85.213.174]:38756 "EHLO mail-yx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750998Ab2FSObg convert rfc822-to-8bit (ORCPT ); Tue, 19 Jun 2012 10:31:36 -0400 MIME-Version: 1.0 In-Reply-To: <4FDC28F0.8050805@jp.fujitsu.com> References: <1339761611-29033-1-git-send-email-handai.szj@taobao.com> <1339761717-29070-1-git-send-email-handai.szj@taobao.com> <4FDC28F0.8050805@jp.fujitsu.com> Date: Tue, 19 Jun 2012 22:31:35 +0800 Message-ID: Subject: Re: [PATCH 2/2] memcg: add per cgroup dirty pages accounting From: Sha Zhengju To: Kamezawa Hiroyuki Cc: Greg Thelen , linux-mm@kvack.org, cgroups@vger.kernel.org, yinghan@google.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, mhocko@suse.cz, Sha Zhengju Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4340 Lines: 110 On Sat, Jun 16, 2012 at 2:34 PM, Kamezawa Hiroyuki wrote: > (2012/06/16 0:32), Greg Thelen wrote: >> >> On Fri, Jun 15 2012, Sha Zhengju wrote: >> >>> This patch adds memcg routines to count dirty pages. I notice that >>> the list has talked about per-cgroup dirty page limiting >>> (http://lwn.net/Articles/455341/) before, but it did not get merged. >> >> >> Good timing, I was just about to make another effort to get some of >> these patches upstream. ?Like you, I was going to start with some basic >> counters. >> >> Your approach is similar to what I have in mind. ?While it is good to >> use the existing PageDirty flag, rather than introducing a new >> page_cgroup flag, there are locking complications (see below) to handle >> races between moving pages between memcg and the pages being {un}marked >> dirty. >> >>> I've no idea how is this going now, but maybe we can add per cgroup >>> dirty pages accounting first. This allows the memory controller to >>> maintain an accurate view of the amount of its memory that is dirty >>> and can provide some infomation while group's direct reclaim is working. >>> >>> After commit 89c06bd5 (memcg: use new logic for page stat accounting), >>> we do not need per page_cgroup flag anymore and can directly use >>> struct page flag. >>> >>> >>> Signed-off-by: Sha Zhengju >>> --- >>> ?include/linux/memcontrol.h | ? ?1 + >>> ?mm/filemap.c ? ? ? ? ? ? ? | ? ?1 + >>> ?mm/memcontrol.c ? ? ? ? ? ?| ? 32 +++++++++++++++++++++++++------- >>> ?mm/page-writeback.c ? ? ? ?| ? ?2 ++ >>> ?mm/truncate.c ? ? ? ? ? ? ?| ? ?1 + >>> ?5 files changed, 30 insertions(+), 7 deletions(-) >>> >>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >>> index a337c2e..8154ade 100644 >>> --- a/include/linux/memcontrol.h >>> +++ b/include/linux/memcontrol.h >>> @@ -39,6 +39,7 @@ enum mem_cgroup_stat_index { >>> ? ? ? ?MEM_CGROUP_STAT_FILE_MAPPED, ?/* # of pages charged as file rss */ >>> ? ? ? ?MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */ >>> ? ? ? ?MEM_CGROUP_STAT_DATA, /* end of data requires synchronization */ >>> + ? ? ? MEM_CGROUP_STAT_FILE_DIRTY, ?/* # of dirty pages in page cache */ >>> ? ? ? ?MEM_CGROUP_STAT_NSTATS, >>> ?}; >>> >>> diff --git a/mm/filemap.c b/mm/filemap.c >>> index 79c4b2b..5b5c121 100644 >>> --- a/mm/filemap.c >>> +++ b/mm/filemap.c >>> @@ -141,6 +141,7 @@ void __delete_from_page_cache(struct page *page) >>> ? ? ? ? * having removed the page entirely. >>> ? ? ? ? */ >>> ? ? ? ?if (PageDirty(page)&& ?mapping_cap_account_dirty(mapping)) { >>> + ? ? ? ? ? ? ? mem_cgroup_dec_page_stat(page, >>> MEM_CGROUP_STAT_FILE_DIRTY); >> >> >> You need to use mem_cgroup_{begin,end}_update_page_stat around critical >> sections that: >> 1) check PageDirty >> 2) update MEM_CGROUP_STAT_FILE_DIRTY counter >> >> This protects against the page from being moved between memcg while >> accounting. ?Same comment applies to all of your new calls to >> mem_cgroup_{dec,inc}_page_stat. ?For usage pattern, see >> page_add_file_rmap. >> > > If you feel some difficulty with mem_cgroup_{begin,end}_update_page_stat(), > please let me know...I hope they should work enough.... > Hi, Kame While digging into the bigger lock of mem_cgroup_{begin,end}_update_page_stat(), I find the reality is more complex than I thought. Simply stated, modifying page info and update page stat may be wide apart and in different level (eg. mm&fs), so if we use the big lock it may lead to scalability and maintainability issues. For example: mem_cgroup_begin_update_page_stat() modify page information => TestSetPageDirty in ceph_set_page_dirty() (fs/ceph/addr.c) XXXXXX => other fs operations mem_cgroup_update_page_stat() => account_page_dirtied() in mm/page-writeback.c mem_cgroup_end_update_page_stat(). We can choose to get lock in higher level meaning vfs set_page_dirty() but this may span too much and can also have some missing cases. What's your opinion of this problem? Thanks, Sha -- 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/