On Wed, Sep 18, 2013 at 02:04:55PM -0400, Johannes Weiner wrote: > On Wed, Sep 18, 2013 at 04:03:04PM +0200, azurIt wrote: > > > CC: "Johannes Weiner" <hannes@xxxxxxxxxxx>, "Andrew Morton" <akpm@xxxxxxxxxxxxxxxxxxxx>, "David Rientjes" <rientjes@xxxxxxxxxx>, "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@xxxxxxxxxxxxxx>, "KOSAKI Motohiro" <kosaki.motohiro@xxxxxxxxxxxxxx>, linux-mm@xxxxxxxxx, cgroups@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx > > >On Tue 17-09-13 13:15:35, azurIt wrote: > > >[...] > > >> Is something unusual on this stack? > > >> > > >> > > >> [<ffffffff810d1a5e>] dump_header+0x7e/0x1e0 > > >> [<ffffffff810d195f>] ? find_lock_task_mm+0x2f/0x70 > > >> [<ffffffff810d1f25>] oom_kill_process+0x85/0x2a0 > > >> [<ffffffff810d24a8>] mem_cgroup_out_of_memory+0xa8/0xf0 > > >> [<ffffffff8110fb76>] mem_cgroup_oom_synchronize+0x2e6/0x310 > > >> [<ffffffff8110efc0>] ? mem_cgroup_uncharge_page+0x40/0x40 > > >> [<ffffffff810d2703>] pagefault_out_of_memory+0x13/0x130 > > >> [<ffffffff81026f6e>] mm_fault_error+0x9e/0x150 > > >> [<ffffffff81027424>] do_page_fault+0x404/0x490 > > >> [<ffffffff810f952c>] ? do_mmap_pgoff+0x3dc/0x430 > > >> [<ffffffff815cb87f>] page_fault+0x1f/0x30 > > > > > >This is a regular memcg OOM killer. Which dumps messages about what is > > >going to do. So no, nothing unusual, except if it was like that for ever > > >which would mean that oom_kill_process is in the endless loop. But a > > >single stack doesn't tell us much. > > > > > >Just a note. When you see something hogging a cpu and you are not sure > > >whether it might be in an endless loop inside the kernel it makes sense > > >to take several snaphosts of the stack trace and see if it changes. If > > >not and the process is not sleeping (there is no schedule on the trace) > > >then it might be looping somewhere waiting for Godot. If it is sleeping > > >then it is slightly harder because you would have to identify what it is > > >waiting for which requires to know a deeper context. > > >-- > > >Michal Hocko > > >SUSE Labs > > > > > > > > I was finally able to get stack of problematic process :) I saved it two times from the same process, as Michal suggested (i wasn't able to take more). Here it is: > > > > First (doesn't look very helpfull): > > [<ffffffffffffffff>] 0xffffffffffffffff > > > > > > Second: > > [<ffffffff810e17d1>] shrink_zone+0x481/0x650 > > [<ffffffff810e2ade>] do_try_to_free_pages+0xde/0x550 > > [<ffffffff810e310b>] try_to_free_pages+0x9b/0x120 > > [<ffffffff81148ccd>] free_more_memory+0x5d/0x60 > > [<ffffffff8114931d>] __getblk+0x14d/0x2c0 > > [<ffffffff8114c973>] __bread+0x13/0xc0 > > [<ffffffff811968a8>] ext3_get_branch+0x98/0x140 > > [<ffffffff81197497>] ext3_get_blocks_handle+0xd7/0xdc0 > > [<ffffffff81198244>] ext3_get_block+0xc4/0x120 > > [<ffffffff81155b8a>] do_mpage_readpage+0x38a/0x690 > > [<ffffffff81155ffb>] mpage_readpages+0xfb/0x160 > > [<ffffffff811972bd>] ext3_readpages+0x1d/0x20 > > [<ffffffff810d9345>] __do_page_cache_readahead+0x1c5/0x270 > > [<ffffffff810d9411>] ra_submit+0x21/0x30 > > [<ffffffff810cfb90>] filemap_fault+0x380/0x4f0 > > [<ffffffff810ef908>] __do_fault+0x78/0x5a0 > > [<ffffffff810f2b24>] handle_pte_fault+0x84/0x940 > > [<ffffffff810f354a>] handle_mm_fault+0x16a/0x320 > > [<ffffffff8102715b>] do_page_fault+0x13b/0x490 > > [<ffffffff815cb87f>] page_fault+0x1f/0x30 > > [<ffffffffffffffff>] 0xffffffffffffffff > > Ah, crap. I'm sorry. You even showed us this exact trace before in > another context, but I did not fully realize what __getblk() is doing. > > My subsequent patches made a charge attempt return -ENOMEM without > reclaim if the memcg is under OOM. And so the reason you have these > reclaim livelocks is because __getblk never fails on -ENOMEM. When > the allocation returns -ENOMEM, it invokes GLOBAL DIRECT RECLAIM and > tries again in an endless loop. The memcg code would previously just > loop inside the charge, reclaiming and killing, until the allocation > succeeded. But the new code relies on the fault stack being unwound > to complete the OOM kill. And since the stack is not unwound with > __getblk() looping around the allocation there is no more memcg > reclaim AND no memcg OOM kill, thus no chance of exiting. > > That code is weird but really old, so it may take a while to evaluate > all the callers as to whether this can be changed. > > In the meantime, I would just allow __getblk to bypass the memcg limit > when it still can't charge after reclaim. Does the below get your > machine back on track? Scratch that. The idea is reasonable but the implementation is not fully cooked yet. I'll send you an update. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
