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

[azurIt]

>On Mon, Sep 09, 2013 at 09:59:17PM +0200, azurIt wrote:
>> >On Mon, Sep 09, 2013 at 03:10:10PM +0200, azurIt wrote:
>> >> >Hi azur,
>> >> >
>> >> >On Wed, Sep 04, 2013 at 10:18:52AM +0200, azurIt wrote:
>> >> >> > CC: "Andrew Morton" <akpm@xxxxxxxxxxxxxxxxxxxx>, "Michal Hocko" <mhocko@xxxxxxx>, "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
>> >> >> >Hello azur,
>> >> >> >
>> >> >> >On Mon, Sep 02, 2013 at 12:38:02PM +0200, azurIt wrote:
>> >> >> >> >>Hi azur,
>> >> >> >> >>
>> >> >> >> >>here is the x86-only rollup of the series for 3.2.
>> >> >> >> >>
>> >> >> >> >>Thanks!
>> >> >> >> >>Johannes
>> >> >> >> >>---
>> >> >> >> >
>> >> >> >> >
>> >> >> >> >Johannes,
>> >> >> >> >
>> >> >> >> >unfortunately, one problem arises: I have (again) cgroup which cannot be deleted :( it's a user who had very high memory usage and was reaching his limit very often. Do you need any info which i can gather now?
>> >> >> >
>> >> >> >Did the OOM killer go off in this group?
>> >> >> >
>> >> >> >Was there a warning in the syslog ("Fixing unhandled memcg OOM
>> >> >> >context")?
>> >> >> 
>> >> >> 
>> >> >> 
>> >> >> Ok, i see this message several times in my syslog logs, one of them is also for this unremovable cgroup (but maybe all of them cannot be removed, should i try?). Example of the log is here (don't know where exactly it starts and ends so here is the full kernel log):
>> >> >> http://watchdog.sk/lkml/oom_syslog.gz
>> >> >There is an unfinished OOM invocation here:
>> >> >
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715112] Fixing unhandled memcg OOM context set up from:
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715191]  [<ffffffff811105c2>] T.1154+0x622/0x8f0
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715274]  [<ffffffff8111153e>] mem_cgroup_cache_charge+0xbe/0xe0
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715357]  [<ffffffff810cf31c>] add_to_page_cache_locked+0x4c/0x140
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715443]  [<ffffffff810cf432>] add_to_page_cache_lru+0x22/0x50
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715526]  [<ffffffff810cfdd3>] find_or_create_page+0x73/0xb0
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715608]  [<ffffffff811493ba>] __getblk+0xea/0x2c0
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715692]  [<ffffffff8114ca73>] __bread+0x13/0xc0
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715774]  [<ffffffff81196968>] ext3_get_branch+0x98/0x140
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715859]  [<ffffffff81197557>] ext3_get_blocks_handle+0xd7/0xdc0
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.715942]  [<ffffffff81198304>] ext3_get_block+0xc4/0x120
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716023]  [<ffffffff81155c3a>] do_mpage_readpage+0x38a/0x690
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716107]  [<ffffffff81155f8f>] mpage_readpage+0x4f/0x70
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716188]  [<ffffffff811973a8>] ext3_readpage+0x28/0x60
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716268]  [<ffffffff810cfa48>] filemap_fault+0x308/0x560
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716350]  [<ffffffff810ef898>] __do_fault+0x78/0x5a0
>> >> >  Aug 22 13:15:21 server01 kernel: [1251422.716433]  [<ffffffff810f2ab4>] handle_pte_fault+0x84/0x940
>> >> >
>> >> >__getblk() has this weird loop where it tries to instantiate the page,
>> >> >frees memory on failure, then retries.  If the memcg goes OOM, the OOM
>> >> >path might be entered multiple times and each time leak the memcg
>> >> >reference of the respective previous OOM invocation.
>> >> >
>> >> >There are a few more find_or_create() sites that do not propagate an
>> >> >error and it's incredibly hard to find out whether they are even taken
>> >> >during a page fault.  It's not practical to annotate them all with
>> >> >memcg OOM toggles, so let's just catch all OOM contexts at the end of
>> >> >handle_mm_fault() and clear them if !VM_FAULT_OOM instead of treating
>> >> >this like an error.
>> >> >
>> >> >azur, here is a patch on top of your modified 3.2.  Note that Michal
>> >> >might be onto something and we are looking at multiple issues here,
>> >> >but the log excert above suggests this fix is required either way.
>> >> 
>> >> 
>> >> 
>> >> 
>> >> Johannes, is this still up to date? Thank you.
>> >
>> >No, please use the following on top of 3.2 (i.e. full replacement, not
>> >incremental to what you have):
>> 
>> 
>> 
>> Unfortunately it didn't compile:
>> 
>> 
>> 
>> 
>>   LD      vmlinux.o
>>   MODPOST vmlinux.o
>> WARNING: modpost: Found 4924 section mismatch(es).
>> To see full details build your kernel with:
>> 'make CONFIG_DEBUG_SECTION_MISMATCH=y'
>>   GEN     .version
>>   CHK     include/generated/compile.h
>>   UPD     include/generated/compile.h
>>   CC      init/version.o
>>   LD      init/built-in.o
>>   LD      .tmp_vmlinux1
>> arch/x86/built-in.o: In function `do_page_fault':
>> (.text+0x26a77): undefined reference to `handle_mm_fault'
>> mm/built-in.o: In function `fixup_user_fault':
>> (.text+0x224d3): undefined reference to `handle_mm_fault'
>> mm/built-in.o: In function `__get_user_pages':
>> (.text+0x24a0f): undefined reference to `handle_mm_fault'
>> make: *** [.tmp_vmlinux1] Error 1
>
>Oops, sorry about that.  Must be configuration dependent because it
>works for me (and handle_mm_fault is obviously defined).
>
>Do you have warnings earlier in the compilation?  You can use make -s
>to filter out everything but warnings.
>
>Or send me your configuration so I can try to reproduce it here.
>
>Thanks!


Johannes,

the server went down early in the morning, the symptoms were similar as before - huge I/O. Can't tell what exactly happened since I wasn't able to login even on the console. But I have some info:
 - applications were able to write to HDD so it wasn't deadlocked as before
 - here is how it looked on graphs: http://watchdog.sk/lkml/graphs.jpg
 - server wasn't responding from 6:36, it was down between 6:54 and 7:02 (i had to hard reboot it), I was awoken at 6:36 by really creepy sound from my phone ;)
 - my 'load check' script successfully killed apache at 6:41 but it didn't help as you can see
 - i have one screen with info from atop from time 6:44, looks like i/o was done by init (??!): http://watchdog.sk/lkml/atop.jpg (ignore swap warning, i have no swap)
 - also other type of logs are available
 - nothing like this happened before

What do you think? I'm now running kernel with your previous patch, not with the newest one.


azur
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