linux-kernel - Re: abnormal OOM killer message

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Date:	Wed, 19 Aug 2009 11:44:08 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	우충기 <chungki.woo@...il.com>,
	Nitin Gupta <ngupta@...are.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	fengguang.wu@...el.com, riel@...hat.com, akpm@...ux-foundation.org,
	kosaki.motohiro@...fujitsu.com, minchan.kim@...il.com,
	Mel Gorman <mel@....ul.ie>
Subject: Re: abnormal OOM killer message

On Wed, 19 Aug 2009 10:41:51 +0900
우충기 <chungki.woo@...il.com> wrote:

> Hi all~
> I have got a log message with OOM below. I don't know why this
> phenomenon was happened.
> When direct reclaim routine(try_to_free_pages) in __alloc_pages which
> allocates kernel memory was failed,
> one last chance is given to allocate memory before OOM routine is executed.
> And that time, allocator uses ALLOC_WMARK_HIGH to limit watermark.
> Then, zone_watermark_ok function test this value with current memory
> state and decide 'can allocate' or 'cannot allocate'.
> 
> Here is some kernel source code in __alloc_pages function to understand easily.
> Kernel version is 2.6.18 for arm11. Memory size is 32Mbyte. And I use
> compcache(0.5.2).
> -------------------------------------------------------------------------------------------------------------------------------------------------------------
>         ...
>         did_some_progress = try_to_free_pages(zonelist->zones,
> gfp_mask);            <== direct page reclaim
> 
>         p->reclaim_state = NULL;
>         p->flags &= ~PF_MEMALLOC;
> 
>         cond_resched();
> 
>         if (likely(did_some_progress)) {
>                 page = get_page_from_freelist(gfp_mask, order,
>                                                 zonelist, alloc_flags);
>                 if (page)
>                         goto got_pg;
>         } else if ((gfp_mask & __GFP_FS) && !(gfp_mask &
> __GFP_NORETRY)) {    <== when fail to reclaim
>                 /*
>                  * Go through the zonelist yet one more time, keep
>                  * very high watermark here, this is only to catch
>                  * a parallel oom killing, we must fail if we're still
>                  * under heavy pressure.
>                  */
>                 page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL,
> order,  <== this is last chance
>                                 zonelist,
> ALLOC_WMARK_HIGH|ALLOC_CPUSET);               <== uses
> ALLOC_WMARK_HIGH
>                 if (page)
>                         goto got_pg;
> 
>                 out_of_memory(zonelist, gfp_mask, order);
>                 goto restart;
>         }
>         ...
> -------------------------------------------------------------------------------------------------------------------------------------------------------------
> 
> In my case, you can see free pages(6804KB) is much more higher than
> high watermark value(1084KB) in OOM message.
> And order of allocating is also zero.(order=0)
> In buddy system, the number of 4kbyte page is 867.
> So, I think OOM can't be happend.
> 

Yes. I think so. 

In that case, even we can also avoid zone defensive algorithm.

> How do you think about this?
> Is this side effect of compcache?

I don't know compcache well.
But I doubt it. Let's Cced Nitin. 

> Please explain me.
> Thanks.
> 
> This is OOM message.
> -------------------------------------------------------------------------------------------------------------------------------------------------------------
> oom-killer: gfp_mask=0x201d2, order=0       (==> __GFP_HIGHMEM,
> __GFP_WAIT, __GFP_IO, __GFP_FS, __GFP_COLD)
> [<c00246c0>] (dump_stack+0x0/0x14) from [<c006ba68>] (out_of_memory+0x38/0x1d0)
> [<c006ba30>] (out_of_memory+0x0/0x1d0) from [<c006d4cc>]
> (__alloc_pages+0x244/0x2c4)
> [<c006d288>] (__alloc_pages+0x0/0x2c4) from [<c006f054>]
> (__do_page_cache_readahead+0x12c/0x2d4)
> [<c006ef28>] (__do_page_cache_readahead+0x0/0x2d4) from [<c006f594>]
> (do_page_cache_readahead+0x60/0x64)
> [<c006f534>] (do_page_cache_readahead+0x0/0x64) from [<c006ac24>]
> (filemap_nopage+0x1b4/0x438)
>  r7 = C0D8C320  r6 = C1422000  r5 = 00000001  r4 = 00000000
> [<c006aa70>] (filemap_nopage+0x0/0x438) from [<c0075684>]
> (__handle_mm_fault+0x398/0xb84)
> [<c00752ec>] (__handle_mm_fault+0x0/0xb84) from [<c0027614>]
> (do_page_fault+0xe8/0x224)
> [<c002752c>] (do_page_fault+0x0/0x224) from [<c0027900>]
> (do_DataAbort+0x3c/0xa0)
> [<c00278c4>] (do_DataAbort+0x0/0xa0) from [<c001fde0>]
> (ret_from_exception+0x0/0x10)
>  r8 = BE9894B8  r7 = 00000078  r6 = 00000130  r5 = 00000000
>  r4 = FFFFFFFF
> Mem-info:
> DMA per-cpu:
> cpu 0 hot: high 6, batch 1 used:0
> cpu 0 cold: high 2, batch 1 used:1
> DMA32 per-cpu: empty
> Normal per-cpu: empty
> HighMem per-cpu: empty
> Free pages:        6804kB (0kB HighMem)
> Active:101 inactive:1527 dirty:0 writeback:0 unstable:0 free:1701
> slab:936 mapped:972 pagetables:379
> DMA free:6804kB min:724kB low:904kB high:1084kB active:404kB
> inactive:6108kB present:32768kB pages_scanned:0 all_unreclaimable? no
> lowmem_reserve[]: 0 0 0 0
> DMA32 free:0kB min:0kB low:0kB high:0kB active:0kB inactive:0kB
> present:0kB pages_scanned:0 all_unreclaimable? no
> lowmem_reserve[]: 0 0 0 0
> Normal free:0kB min:0kB low:0kB high:0kB active:0kB inactive:0kB
> present:0kB pages_scanned:0 all_unreclaimable? no
> lowmem_reserve[]: 0 0 0 0
> HighMem free:0kB min:128kB low:128kB high:128kB active:0kB
> inactive:0kB present:0kB pages_scanned:0 all_unreclaimable? no
> lowmem_reserve[]: 0 0 0 0
> DMA: 867*4kB 273*8kB 36*16kB 2*32kB 0*64kB 0*128kB 0*256kB 1*512kB
> 0*1024kB 0*2048kB 0*4096kB = 6804kB
> DMA32: empty
> Normal: empty
> HighMem: empty
> Swap cache: add 4597, delete 4488, find 159/299, race 0+0
> Free swap  = 67480kB
> Total swap = 81916kB

In addition, total swap : 79M?? 

> Free swap:        67480kB
> 8192 pages of RAM
> 1960 free pages
> 978 reserved pages
> 936 slab pages
> 1201 pages shared
> 109 pages swap cached

free page : 6M
page table + slab + reserved : 8M
active + inacive : 6M

Where is 12M? 

> Out of Memory: Kill process 47 (rc.local) score 849737 and children.
> Out of memory: Killed process 49 (CTaskManager).
> Killed
> SW image is stopped..
> script in BOOT is stopped...
> Starting pid 348, console /dev/ttyS1: '/bin/sh'
> -sh: id: not found
> #
> -------------------------------------------------------------------------------------------------------------------------------------------------------------

As you mentioned, your memory size is 32M and you use compcache.
How is swap size bigger than your memory size ?
Is the result of compression of swap pages ? 
Nitin. Could you answer the question?

I can't imagine whey order 0 allocation failed although there are
many pages in buddy. 

What do you mm guys think about this problem ?

-- 
Kind regards,
Minchan Kim
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