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: > [<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. > > 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
