From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx104.postini.com [74.125.245.104]) by kanga.kvack.org (Postfix) with SMTP id 5488A6B0005 for ; Wed, 6 Feb 2013 09:22:23 -0500 (EST) Date: Wed, 6 Feb 2013 15:22:19 +0100 From: Michal Hocko Subject: Re: [PATCH for 3.2.34] memcg: do not trigger OOM from add_to_page_cache_locked Message-ID: <20130206142219.GF10254@dhcp22.suse.cz> References: <20121228162209.GA1455@dhcp22.suse.cz> <20121230020947.AA002F34@pobox.sk> <20121230110815.GA12940@dhcp22.suse.cz> <20130125160723.FAE73567@pobox.sk> <20130125163130.GF4721@dhcp22.suse.cz> <20130205134937.GA22804@dhcp22.suse.cz> <20130205154947.CD6411E2@pobox.sk> <20130205160934.GB22804@dhcp22.suse.cz> <20130206021721.1AE9E3C7@pobox.sk> <20130206140119.GD10254@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130206140119.GD10254@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: azurIt Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups mailinglist , KAMEZAWA Hiroyuki , Johannes Weiner On Wed 06-02-13 15:01:19, Michal Hocko wrote: > On Wed 06-02-13 02:17:21, azurIt wrote: > > >5-memcg-fix-1.patch is not complete. It doesn't contain the folloup I > > >mentioned in a follow up email. Here is the full patch: > > > > > > Here is the log where OOM, again, killed MySQL server [search for "(mysqld)"]: > > http://www.watchdog.sk/lkml/oom_mysqld6 > > [...] > WARNING: at mm/memcontrol.c:2409 T.1149+0x2d9/0x610() > Hardware name: S5000VSA > gfp_mask:4304 nr_pages:1 oom:0 ret:2 > Pid: 3545, comm: apache2 Tainted: G W 3.2.37-grsec #1 > Call Trace: > [] warn_slowpath_common+0x7a/0xb0 > [] warn_slowpath_fmt+0x46/0x50 > [] ? mem_cgroup_margin+0x73/0xa0 > [] T.1149+0x2d9/0x610 > [] ? blk_finish_plug+0x18/0x50 > [] mem_cgroup_cache_charge+0xc4/0xf0 > [] add_to_page_cache_locked+0x4f/0x140 > [] add_to_page_cache_lru+0x22/0x50 > [] filemap_fault+0x252/0x4f0 > [] __do_fault+0x78/0x5a0 > [] handle_pte_fault+0x84/0x940 > [] ? vma_prio_tree_insert+0x30/0x50 > [] ? vma_link+0x88/0xe0 > [] handle_mm_fault+0x138/0x260 > [] do_page_fault+0x13d/0x460 > [] ? do_mmap_pgoff+0x3dc/0x430 > [] page_fault+0x1f/0x30 > ---[ end trace 8817670349022007 ]--- > apache2 invoked oom-killer: gfp_mask=0x0, order=0, oom_adj=0, oom_score_adj=0 > apache2 cpuset=uid mems_allowed=0 > Pid: 3545, comm: apache2 Tainted: G W 3.2.37-grsec #1 > Call Trace: > [] dump_header+0x7e/0x1e0 > [] ? find_lock_task_mm+0x2f/0x70 > [] oom_kill_process+0x85/0x2a0 > [] out_of_memory+0xe5/0x200 > [] pagefault_out_of_memory+0xbd/0x110 > [] mm_fault_error+0xb6/0x1a0 > [] do_page_fault+0x3ee/0x460 > [] ? do_mmap_pgoff+0x3dc/0x430 > [] page_fault+0x1f/0x30 > > The first trace comes from the debugging WARN and it clearly points to > a file fault path. __do_fault pre-charges a page in case we need to > do CoW (copy-on-write) for the returned page. This one falls back to > memcg OOM and never returns ENOMEM as I have mentioned earlier. > However, the fs fault handler (filemap_fault here) can fallback to > page_cache_read if the readahead (do_sync_mmap_readahead) fails > to get page to the page cache. And we can see this happening in > the first trace. page_cache_read then calls add_to_page_cache_lru > and eventually gets to add_to_page_cache_locked which calls > mem_cgroup_cache_charge_no_oom so we will get ENOMEM if oom should > happen. This ENOMEM gets to the fault handler and kaboom. > > So the fix is really much more complex than I thought. Although > add_to_page_cache_locked sounded like a good place it turned out to be > not in fact. > > We need something more clever appaerently. One way would be not misusing > __GFP_NORETRY for GFP_MEMCG_NO_OOM and give it a real flag. We have 32 > bits for those flags in gfp_t so there should be some room there. > Or we could do this per task flag, same we do for NO_IO in the current > -mm tree. > The later one seems easier wrt. gfp_mask passing horror - e.g. > __generic_file_aio_write doesn't pass flags and it can be called from > unlocked contexts as well. Ouch, PF_ flags space seem to be drained already because task_struct::flags is just unsigned int so there is just one bit left. I am not sure this is the best use for it. This will be a real pain! -- Michal Hocko SUSE Labs -- 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