> CC: "Michal Hocko" <mhocko@xxxxxxx>, "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 Wed, Sep 18, 2013 at 02:19:46PM -0400, Johannes Weiner wrote: >> 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. > >Here is an update. Full replacement on top of 3.2 since we tried a >dead end and it would be more painful to revert individual changes. > >The first bug you had was the same task entering OOM repeatedly and >leaking the memcg reference, thus creating undeletable memcgs. My >fixup added a condition that if the task already set up an OOM context >in that fault, another charge attempt would immediately return -ENOMEM >without even trying reclaim anymore. This dropped __getblk() into an >endless loop of waking the flushers and performing global reclaim and >memcg returning -ENOMEM regardless of free memory. > >The update now basically only changes this -ENOMEM to bypass, so that >the memory is not accounted and the limit ignored. OOM killed tasks >are granted the same right, so that they can exit quickly and release >memory. Likewise, we want a task that hit the OOM condition also to >finish the fault quickly so that it can invoke the OOM killer. > >Does the following work for you, azur? Johannes, bad news everyone! :( Unfortunaely, two different problems appears today: 1.) This looks like my very original problem - stucked processes inside one cgroup. I took stacks from all of them over time but server was very slow so i had to kill them soon: http://watchdog.sk/lkmlmemcg-bug-9.tar.gz 2.) This was just like my last problem where few processes were doing huge i/o. As sever was almost unoperable i barely killed them so no more info here, sorry. azur -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>