Re: [PATCH for 3.2.34] memcg: do not trigger OOM from add_to_page_cache_locked

[Kamezawa Hiroyuki]

(2013/02/07 21:31), Michal Hocko wrote:
> On Thu 07-02-13 20:01:45, KAMEZAWA Hiroyuki wrote:
> > (2013/02/06 23:01), 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:
> > >   [<ffffffff8105502a>] warn_slowpath_common+0x7a/0xb0
> > >   [<ffffffff81055116>] warn_slowpath_fmt+0x46/0x50
> > >   [<ffffffff81108163>] ? mem_cgroup_margin+0x73/0xa0
> > >   [<ffffffff8110b6f9>] T.1149+0x2d9/0x610
> > >   [<ffffffff812af298>] ? blk_finish_plug+0x18/0x50
> > >   [<ffffffff8110c6b4>] mem_cgroup_cache_charge+0xc4/0xf0
> > >   [<ffffffff810ca6bf>] add_to_page_cache_locked+0x4f/0x140
> > >   [<ffffffff810ca7d2>] add_to_page_cache_lru+0x22/0x50
> > >   [<ffffffff810cad32>] filemap_fault+0x252/0x4f0
> > >   [<ffffffff810eab18>] __do_fault+0x78/0x5a0
> > >   [<ffffffff810edcb4>] handle_pte_fault+0x84/0x940
> > >   [<ffffffff810e2460>] ? vma_prio_tree_insert+0x30/0x50
> > >   [<ffffffff810f2508>] ? vma_link+0x88/0xe0
> > >   [<ffffffff810ee6a8>] handle_mm_fault+0x138/0x260
> > >   [<ffffffff8102709d>] do_page_fault+0x13d/0x460
> > >   [<ffffffff810f46fc>] ? do_mmap_pgoff+0x3dc/0x430
> > >   [<ffffffff815b61ff>] 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:
> > >   [<ffffffff810ccd2e>] dump_header+0x7e/0x1e0
> > >   [<ffffffff810ccc2f>] ? find_lock_task_mm+0x2f/0x70
> > >   [<ffffffff810cd1f5>] oom_kill_process+0x85/0x2a0
> > >   [<ffffffff810cd8a5>] out_of_memory+0xe5/0x200
> > >   [<ffffffff810cda7d>] pagefault_out_of_memory+0xbd/0x110
> > >   [<ffffffff81026e76>] mm_fault_error+0xb6/0x1a0
> > >   [<ffffffff8102734e>] do_page_fault+0x3ee/0x460
> > >   [<ffffffff810f46fc>] ? do_mmap_pgoff+0x3dc/0x430
> > >   [<ffffffff815b61ff>] 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.
> >
> > Hmm. do we need to increase the "limit" virtually at memcg oom until
> > the oom-killed process dies ? It may be doable by increasing stock->cache
> > of each cpu....I think kernel can offer extra virtual charge up to
> > oom-killed process's memory usage.....
>
> If we can guarantee that the overflow charges do not exceed the memory
> usage of the killed process then this would work. The question is, how
> do we find out how much we can overflow. immigrate_on_move will play
> some role as well as the amount of the shared memory. I am afraid this
> would get too complex. Nevertheless the idea is nice.
Yes, that's the problem. If we don't do in correct way, resouce usage
undeflow can happen. I guess we can count it per task_struct at charging
page-faulted anon pages.

_Or_ in other consideration, for example, we do charge 1MB per thread
regardless of its memory usage. And use it as a security at OOM-killing.
Implemtation will be easy but explanation may be difficult..

Thanks,
-Kame




Thanks,
-Kame



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