Re: [patch 0/7] improve memcg oom killer robustness v2

["azurIt" <azurit@pobox.sk>]

>Hi azur,
>
>On Mon, Oct 07, 2013 at 01:01:49PM +0200, azurIt wrote:
>> >On Thu, Sep 26, 2013 at 06:54:59PM +0200, azurIt wrote:
>> >> On Wed, Sep 18, 2013 at 02:19:46PM -0400, Johannes Weiner wrote:
>> >> >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.
>> >
>> >From one of the tasks:
>> >
>> >1380213238/11210/stack:[<ffffffff810528f1>] sys_sched_yield+0x41/0x70
>> >1380213238/11210/stack:[<ffffffff81148ef1>] free_more_memory+0x21/0x60
>> >1380213238/11210/stack:[<ffffffff8114957d>] __getblk+0x14d/0x2c0
>> >1380213238/11210/stack:[<ffffffff81198a2b>] ext3_getblk+0xeb/0x240
>> >1380213238/11210/stack:[<ffffffff8119d2df>] ext3_find_entry+0x13f/0x480
>> >1380213238/11210/stack:[<ffffffff8119dd6d>] ext3_lookup+0x4d/0x120
>> >1380213238/11210/stack:[<ffffffff81122a55>] d_alloc_and_lookup+0x45/0x90
>> >1380213238/11210/stack:[<ffffffff81122ff8>] do_lookup+0x278/0x390
>> >1380213238/11210/stack:[<ffffffff81124c40>] path_lookupat+0x120/0x800
>> >1380213238/11210/stack:[<ffffffff81125355>] do_path_lookup+0x35/0xd0
>> >1380213238/11210/stack:[<ffffffff811254d9>] user_path_at_empty+0x59/0xb0
>> >1380213238/11210/stack:[<ffffffff81125541>] user_path_at+0x11/0x20
>> >1380213238/11210/stack:[<ffffffff81115b70>] sys_faccessat+0xd0/0x200
>> >1380213238/11210/stack:[<ffffffff81115cb8>] sys_access+0x18/0x20
>> >1380213238/11210/stack:[<ffffffff815ccc26>] system_call_fastpath+0x18/0x1d
>> >
>> >Should have seen this coming... it's still in that braindead
>> >__getblk() loop, only from a syscall this time (no OOM path).  The
>> >group's memory.stat looks like this:
>> >
>> >cache 0
>> >rss 0
>> >mapped_file 0
>> >pgpgin 0
>> >pgpgout 0
>> >swap 0
>> >pgfault 0
>> >pgmajfault 0
>> >inactive_anon 0
>> >active_anon 0
>> >inactive_file 0
>> >active_file 0
>> >unevictable 0
>> >hierarchical_memory_limit 209715200
>> >hierarchical_memsw_limit 209715200
>> >total_cache 0
>> >total_rss 209715200
>> >total_mapped_file 0
>> >total_pgpgin 1028153297
>> >total_pgpgout 1028102097
>> >total_swap 0
>> >total_pgfault 1352903120
>> >total_pgmajfault 45342
>> >total_inactive_anon 0
>> >total_active_anon 209715200
>> >total_inactive_file 0
>> >total_active_file 0
>> >total_unevictable 0
>> >
>> >with anonymous pages to the limit and you probably don't have any swap
>> >space enabled to anything in the group.
>> >
>> >I guess there is no way around annotating that __getblk() loop.  The
>> >best solution right now is probably to use __GFP_NOFAIL.  For one, we
>> >can let the allocation bypass the memcg limit if reclaim can't make
>> >progress.  But also, the loop is then actually happening inside the
>> >page allocator, where it should happen, and not around ad-hoc direct
>> >reclaim in buffer.c.
>> >
>> >Can you try this on top of our ever-growing stack of patches?
>> 
>> 
>> 
>> 
>> Joahnnes,
>> 
>> looks like the problem is completely resolved :) Thank you, Michal
>> Hocko and everyone involved for help and time.
>
>Thanks a lot for your patience.  I will send out the fixes for 3.12.
>
>> One more thing: I see that your patches are going into 3.12. Is
>> there a chance to get them also into 3.2? Is Ben Hutchings (current
>> maintainer of 3.2 branch) competent to decide this? Should i contact
>> him directly? I can't upgrade to 3.12 because stable grsecurity is
>> for 3.2 and i don't think this will change in near future.
>
>Yes, I'll send them to stable.  The original OOM killer rework was not
>tagged for stable, but since we have a known deadlock problem, I think
>it makes sense to include them after all.



Joahnnes,

i'm very sorry to say it but today something strange happened.. :) i was just right at the computer so i noticed it almost immediately but i don't have much info. Server stoped to respond from the net but i was already logged on ssh which was working quite fine (only a little slow). I was able to run commands on shell but i didn't do much because i was afraid that it will goes down for good soon. I noticed few things:
 - htop was strange because all CPUs were doing nothing (totally nothing)
 - there were enough of free memory
 - server load was about 90 and was raising slowly
 - i didn't see ANY process in 'run' state
 - i also didn't see any process with strange behavior (taking much CPU, memory or so) so it wasn't obvious what to do to fix it
 - i started to kill Apache processes, everytime i killed some, CPUs did some work, but it wasn't fixing the problem
 - finally i did 'skill -kill apache2' in shell and everything started to work
 - server monitoring wasn't sending any data so i have no graphs
 - nothing interesting in logs

I will send more info when i get some.

azur

--
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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>