Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757649Ab2FUH4a (ORCPT ); Thu, 21 Jun 2012 03:56:30 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:48725 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752496Ab2FUH42 (ORCPT ); Thu, 21 Jun 2012 03:56:28 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.7.4 Message-ID: <4FE2D2F4.2020202@jp.fujitsu.com> Date: Thu, 21 Jun 2012 16:53:24 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.0; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Sha Zhengju 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 Subject: Re: [PATCH 2/2] memcg: add per cgroup dirty pages accounting 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> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5366 Lines: 141 (2012/06/19 23:31), Sha Zhengju wrote: > 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? > yes, that's sad....If set_page_dirty() is always called under lock_page(), the story will be easier (we'll take lock_page() in move side.) but the comment on set_page_dirty() says it's not true.....Now, I haven't found a magical way for avoiding the race. (*) If holding lock_page() in move_account() can be a generic solution, it will be good. A proposal from me is a small-start. You can start from adding hooks to a generic functions as set_page_dirty() and __set_page_dirty_nobuffers(), clear_page_dirty_for_io(). And see what happens. I guess we can add WARN_ONCE() against callers of update_page_stat() who don't take mem_cgroup_begin/end_update_page_stat() (by some new check, for example, checking !rcu_read_lock_held() in update_stat()) I think we can make TODO list and catch up remaining things one by one. Thanks, -Kame -- 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/