Re: Found the commit that causes the OOMs

[Minchan Kim]

On Mon, 29 Jun 2009 17:07:25 +0100
Mel Gorman <mel@xxxxxxxxx> wrote:

> On Tue, Jun 30, 2009 at 12:00:26AM +0900, Minchan Kim wrote:
> > On Mon, Jun 29, 2009 at 11:21 PM, David Howells<dhowells@xxxxxxxxxx> wrote:
> > > Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> > >
> > >> Sorry! This one compiles OK:
> > >
> > > Sadly that doesn't seem to work either:
> > >
> > > msgctl11 invoked oom-killer: gfp_mask=0x200da, order=0, oom_adj=0
> > > msgctl11 cpuset=/ mems_allowed=0
> > > Pid: 30858, comm: msgctl11 Not tainted 2.6.31-rc1-cachefs #146
> > > Call Trace:
> > > Â[<ffffffff8107207e>] ? oom_kill_process.clone.0+0xa9/0x245
> > > Â[<ffffffff81072345>] ? __out_of_memory+0x12b/0x142
> > > Â[<ffffffff810723c6>] ? out_of_memory+0x6a/0x94
> > > Â[<ffffffff81074a90>] ? __alloc_pages_nodemask+0x42e/0x51d
> > > Â[<ffffffff81080843>] ? do_wp_page+0x2c6/0x5f5
> > > Â[<ffffffff810820c1>] ? handle_mm_fault+0x5dd/0x62f
> > > Â[<ffffffff81022c32>] ? do_page_fault+0x1f8/0x20d
> > > Â[<ffffffff812e069f>] ? page_fault+0x1f/0x30
> > > Mem-Info:
> > > DMA per-cpu:
> > > CPU Â Â0: hi: Â Â0, btch: Â 1 usd: Â 0
> > > CPU Â Â1: hi: Â Â0, btch: Â 1 usd: Â 0
> > > DMA32 per-cpu:
> > > CPU Â Â0: hi: Â186, btch: Â31 usd: Â38
> > > CPU Â Â1: hi: Â186, btch: Â31 usd: 106
> > > Active_anon:75040 active_file:0 inactive_anon:2031
> > > Âinactive_file:0 unevictable:0 dirty:0 writeback:0 unstable:0
> > > Âfree:1951 slab:41499 mapped:301 pagetables:60674 bounce:0
> > > DMA free:3932kB min:60kB low:72kB high:88kB active_anon:2868kB inactive_anon:384kB active_file:0kB inactive_file:0kB unevictable:0kB present:15364kB pages_scanned:0 all_unreclaimable? no
> > > lowmem_reserve[]: 0 968 968 968
> > > DMA32 free:3872kB min:3948kB low:4932kB high:5920kB active_anon:297292kB inactive_anon:7740kB active_file:0kB inactive_file:0kB unevictable:0kB present:992032kB pages_scanned:0 all_unreclaimable? no
> > > lowmem_reserve[]: 0 0 0 0
> > > DMA: 7*4kB 0*8kB 0*16kB 0*32kB 1*64kB 0*128kB 1*256kB 1*512kB 1*1024kB 1*2048kB 0*4096kB = 3932kB
> > > DMA32: 500*4kB 2*8kB 0*16kB 0*32kB 1*64kB 0*128kB 1*256kB 1*512kB 1*1024kB 0*2048kB 0*4096kB = 3872kB
> > > 1928 total pagecache pages
> > > 0 pages in swap cache
> > > Swap cache stats: add 0, delete 0, find 0/0
> > > Free swap Â= 0kB
> > > Total swap = 0kB
> > > 255744 pages RAM
> > > 5589 pages reserved
> > > 238251 pages shared
> > > 216210 pages non-shared
> > > Out of memory: kill process 25221 (msgctl11) score 130560 or a child
> > > Killed process 26379 (msgctl11)
> > 
> > Totally, I can't understand this situation.
> > Now, this page allocation is order zero and It is just likely GFP_HIGHUSER.
> > So it's unlikely interrupt context.
> 
> The GFP flags that are set are
> 
> #define __GFP_HIGHMEM	(0x02)
> #define __GFP_MOVABLE	(0x08)  /* Page is movable */
> #define __GFP_WAIT	(0x10)	/* Can wait and reschedule? */
> #define __GFP_IO	(0x40)	/* Can start physical IO? */
> #define __GFP_FS	(0x80)	/* Can call down to low-level FS? */
> #define __GFP_HARDWALL   (0x20000) /* Enforce hardwall cpuset memory allocs */
> 
> which are fairly permissive in terms of what action can be taken.
> 
> > Buddy already has enough fallback DMA32, I think.
> 
> It doesn't really. We are below the minimum watermark. It wouldn't be
> able to grant the allocation until a few pages had been freed.

Yes. I missed that. 

> > Why kernel can't allocate page for order 0 ?
> > Is it allocator bug ?
> > 
> 
> If it is, it is not because the allocation failed as the watermarks were not
> being met. For this situation to be occuring, it has to be scanning the LRU
> lists and making no forward progress. Odd things to note;
> 
> o active_anon is very large in comparison to inactive_anon. Is this
>   because there is no swap and they are no longer being rotated?

Yes. My patch's intention was that. 

       commit 69c854817566db82c362797b4a6521d0b00fe1d8
       Author: MinChan Kim <minchan.kim@xxxxxxxxx>
       Date:   Tue Jun 16 15:32:44 2009 -0700

> o Slab and pagetables are very large. Is slab genuinely unshrinkable?
>
> I think this system might be genuinely OOM. It can't reclaim memory and
> we are below the minimum watermarks.
> 
> Is it possible there are pages that are counted as active_anon that in
> fact are reclaimable because they are on the wrong LRU list? If that was
> the case, the lack of rotation to inactive list would prevent them
> getting discovered.

I agree. 
One of them is that "[BUGFIX][PATCH] fix lumpy reclaim lru handiling at
isolate_lru_pages v2" as Kosaki already said. 

Unfortunately, David said it's not. 
But I think your guessing make sense. 

David. Doesn't it happen OOM if you revert my patch, still?


> 
> -- 
> Mel Gorman
> Part-time Phd Student                          Linux Technology Center
> University of Limerick                         IBM Dublin Software Lab


-- 
Kinds Regards
Minchan Kim
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