Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755359Ab1CPVTz (ORCPT ); Wed, 16 Mar 2011 17:19:55 -0400 Received: from smtp-out.google.com ([216.239.44.51]:53827 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754691Ab1CPVTt convert rfc822-to-8bit (ORCPT ); Wed, 16 Mar 2011 17:19:49 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=FPE+4OBDW9sEviy81fMcpbqd5j0AANzUWr6J9itzXpPHruKs39h9Tj2+QpBRbHZ2jh SDrf6MWBVzePeYJoTz6A== MIME-Version: 1.0 In-Reply-To: <20110316131324.GM2140@cmpxchg.org> References: <1299869011-26152-1-git-send-email-gthelen@google.com> <20110311171006.ec0d9c37.akpm@linux-foundation.org> <20110314202324.GG31120@redhat.com> <20110315184839.GB5740@redhat.com> <20110316131324.GM2140@cmpxchg.org> From: Greg Thelen Date: Wed, 16 Mar 2011 14:19:26 -0700 Message-ID: Subject: Re: [PATCH v6 0/9] memcg: per cgroup dirty page accounting To: Johannes Weiner Cc: Vivek Goyal , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, containers@lists.osdl.org, linux-fsdevel@vger.kernel.org, Andrea Righi , Balbir Singh , KAMEZAWA Hiroyuki , Daisuke Nishimura , Minchan Kim , Ciju Rajan K , David Rientjes , Wu Fengguang , Chad Talbott , Justin TerAvest Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5319 Lines: 118 On Wed, Mar 16, 2011 at 6:13 AM, Johannes Weiner wrote: > On Tue, Mar 15, 2011 at 02:48:39PM -0400, Vivek Goyal wrote: >> On Mon, Mar 14, 2011 at 07:41:13PM -0700, Greg Thelen wrote: >> > On Mon, Mar 14, 2011 at 1:23 PM, Vivek Goyal wrote: >> > > On Mon, Mar 14, 2011 at 11:29:17AM -0700, Greg Thelen wrote: >> > > >> > > [..] >> > >> > We could just crawl the memcg's page LRU and bring things under control >> > >> > that way, couldn't we? ?That would fix it. ?What were the reasons for >> > >> > not doing this? >> > >> >> > >> My rational for pursuing bdi writeback was I/O locality. ?I have heard that >> > >> per-page I/O has bad locality. ?Per inode bdi-style writeback should have better >> > >> locality. >> > >> >> > >> My hunch is the best solution is a hybrid which uses a) bdi writeback with a >> > >> target memcg filter and b) using the memcg lru as a fallback to identify the bdi >> > >> that needed writeback. ?I think the part a) memcg filtering is likely something >> > >> like: >> > >> ?http://marc.info/?l=linux-kernel&m=129910424431837 >> > >> >> > >> The part b) bdi selection should not be too hard assuming that page-to-mapping >> > >> locking is doable. >> > > >> > > Greg, >> > > >> > > IIUC, option b) seems to be going through pages of particular memcg and >> > > mapping page to inode and start writeback on particular inode? >> > >> > Yes. >> > >> > > If yes, this might be reasonably good. In the case when cgroups are not >> > > sharing inodes then it automatically maps one inode to one cgroup and >> > > once cgroup is over limit, it starts writebacks of its own inode. >> > > >> > > In case inode is shared, then we get the case of one cgroup writting >> > > back the pages of other cgroup. Well I guess that also can be handeled >> > > by flusher thread where a bunch or group of pages can be compared with >> > > the cgroup passed in writeback structure. I guess that might hurt us >> > > more than benefit us. >> > >> > Agreed. ?For now just writing the entire inode is probably fine. >> > >> > > IIUC how option b) works then we don't even need option a) where an N level >> > > deep cache is maintained? >> > >> > Originally I was thinking that bdi-wide writeback with memcg filter >> > was a good idea. ?But this may be unnecessarily complex. ?Now I am >> > agreeing with you that option (a) may not be needed. ?Memcg could >> > queue per-inode writeback using the memcg lru to locate inodes >> > (lru->page->inode) with something like this in >> > [mem_cgroup_]balance_dirty_pages(): >> > >> > ? while (memcg_usage() >= memcg_fg_limit) { >> > ? ? inode = memcg_dirty_inode(cg); ?/* scan lru for a dirty page, then >> > grab mapping & inode */ >> > ? ? sync_inode(inode, &wbc); >> > ? } >> > >> > ? if (memcg_usage() >= memcg_bg_limit) { >> > ? ? queue per-memcg bg flush work item >> > ? } >> >> I think even for background we shall have to implement some kind of logic >> where inodes are selected by traversing memcg->lru list so that for >> background write we don't end up writting too many inodes from other >> root group in an attempt to meet the low background ratio of memcg. >> >> So to me it boils down to coming up a new inode selection logic for >> memcg which can be used both for background as well as foreground >> writes. This will make sure we don't end up writting pages from the >> inodes we don't want to. > > Originally for struct page_cgroup reduction, I had the idea of > introducing something like > > ? ? ? ?struct memcg_mapping { > ? ? ? ? ? ? ? ?struct address_space *mapping; > ? ? ? ? ? ? ? ?struct mem_cgroup *memcg; > ? ? ? ?}; > > hanging off page->mapping to make memcg association no longer per-page > and save the pc->memcg linkage (it's not completely per-inode either, > multiple memcgs can still refer to a single inode). > > We could put these descriptors on a per-memcg list and write inodes > from this list during memcg-writeback. > > We would have the option of extending this structure to contain hints > as to which subrange of the inode is actually owned by the cgroup, to > further narrow writeback to the right pages - iff shared big files > become a problem. > > Does that sound feasible? If I understand your memcg_mapping proposal, then each inode could have a collection of memcg_mapping objects representing the set of memcg that were charged for caching pages of the inode's data. When a new file page is charged to a memcg, then the inode's set of memcg_mapping would be scanned to determine if current's memcg is already in the memcg_mapping set. If this is the first page for the memcg within the inode, then a new memcg_mapping would be allocated and attached to the inode. The memcg_mapping may be reference counted and would be deleted when the last inode page for a particular memcg is uncharged. page->mapping = &memcg_mapping inode->i_mapping = collection of memcg_mapping, grows/shrinks with [un]charge Am I close? I still have to think though the various use cases, but I wanted to make sure I had the basic idea. -- 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/