linux-kernel - Re: oom_killer crash linux system

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Date:	Tue, 19 Oct 2010 11:59:52 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Figo.zhang" <zhangtianfei@...dcoretech.com>
Cc:	lKOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
	figo1802 <figo1802@...il.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: oom_killer crash linux system

On Tue, 19 Oct 2010 10:07:38 +0800
"Figo.zhang" <zhangtianfei@...dcoretech.com> wrote:

> 
> > 
> > very lots of change ;)
> > can you please send us your crash log?
> 
> i add some prink in select_bad_process() and oom_badness() to see
> pid/totalpages/points/memoryuseage/and finally process to selet to kill.
> 
> i found it the oom-killer select: syslog-ng,mysqld,nautilus,VirtualBox
> to kill, so my question is:
> 
> 1. the syslog-ng,mysqld,nautilus is the system foundamental process, so
> if oom-killer kill those process, the system will be damaged, such as
> lose some important data.
> 
> 2. the new oom-killer just use percentage of used memory as score to
> select the candidate to kill, but how to know this process to very
> important for system?
> 

The kernel can never know it. Just an admin (a man or management software) knows.
Old kernel tries to guess it, but it tend to be wrong and many many report comes
"why my ....is killed..." All guesswork the kernel does is not enough, I think.

> oom_score_adj, it is anyone commercial linux distributions to use this
> to protect the critical process.
> 
oom_adj may be used in some system. All my customers select panic_at_oom=1
and cause cluster fail over rather than half-broken.

<Off topic>
Your another choice is memory cgroup, I think.
please see documentation/cgroup/memory.txt or libcgroup.
http://sourceforge.net/projects/libcg/
You can use some fancy controls with it.
</Off topic>


BTW, there seems to be some strange things.
(CC'ed to linux-mm)
Brief Summary:
   an oom-killer happens on swapless environment with 2.6.36-rc8.
   It has 2G memory.
a reporter says
==
> i want to test the oom-killer. My desktop (Dell optiplex 780, i686
> kernel)have 2GB ram, i turn off the swap partition, and open a huge pdf
> files and applications, and let the system eat huge ram.
> 
> in 2.6.35, i can use ram up to 1.75GB,
> 
> but in 2.6.36-rc8, i just use to 1.53GB ram , the system come very slow
> and crashed after some minutes , the DiskIO is very busy. i see the
> DiskIO read is up to 8MB/s, write just only 400KB/s, (see by conky).
==

The trigger of oom-kill is order=0 allocation. (see original mail for full log)


Oct 19 09:44:08 myhost kernel: [  618.441470] httpd invoked oom-killer:
gfp_mask=0x201da, order=0, oom_adj=0, oom_score_adj=0

Zone's stat is.

Oct 19 09:44:08 myhost kernel: [  618.441551]
DMA free:7968kB min:64kB low:80kB high:96kB active_anon:3700kB inactive_anon:3752kB
    active_file:12kB inactive_file:252kB unevictable:0kB isolated(anon):0kB
    isolated(file):0kB present:15788kB mlocked:0kB dirty:0kB writeback:4kB
    mapped:52kB shmem:348kB slab_reclaimable:0kB slab_unreclaimable:16kB
    kernel_stack:0kB pagetables:0kB unstable:0kB bounce:0kB
    writeback_tmp:0kB pages_scanned:421 all_unreclaimable? yes
    lowmem_reserve[]: 0 865 1980 1980

Oct 19 09:44:08 myhost kernel: [  618.441560]
Normal free:39348kB min:3728kB low:4660kB high:5592kB active_anon:176740kB
       inactive_anon:25640kB active_file:84kB inactive_file:308kB
       unevictable:0kB isolated(anon):0kB isolated(file):0kB present:885944kB
       mlocked:0kB dirty:0kB writeback:4kB mapped:576992kB shmem:5024kB
       slab_reclaimable:7612kB slab_unreclaimable:15512kB kernel_stack:2792kB
       pagetables:6884kB unstable:0kB bounce:0kB writeback_tmp:0kB
       pages_scanned:741 all_unreclaimable? yes
       lowmem_reserve[]: 0 0 8921 8921

Oct 19 09:44:08 myhost kernel: [  618.441569]
HighMem free:392kB min:512kB low:1712kB high:2912kB active_anon:492208kB
        inactive_anon:166404kB active_file:180kB inactive_file:840kB
        unevictable:40kB isolated(anon):0kB isolated(file):0kB present:1141984kB
        mlocked:40kB dirty:0kB writeback:12kB mapped:493648kB shmem:72216kB
        slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB
        pagetables:0kB unstable:0kB bounce:0kB writeback_tmp:0kB
        pages_scanned:1552 all_unreclaimable? yes

Highmem seems a bit strange.
  present(1141984) - active_anon - inactive_anon - inactive_file - active_file
  = 482352kB but free is 392kB.

  Highmem is used for some other purpose than usual user's page.(pagetable is 0.)
  And, Hmm, mapped:493648kB seems too large for me. 
  (active/inactive-file + shmem is not enough.)
  And "mapped" in NORMAL zone is large, too.

  Does anyone have idea about file-mapped-but-not-on-LRU pages ?

Thanks,
-Kame
  





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