Re: [Bugme-new] [Bug 40262] New: PROBLEM: I/O storm from hell on kernel 3.0.0 when touch swap (swapfile or partition)

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Sun, 28 Aug 2011 15:13:35 +0400
Konstantin Khlebnikov <khlebnikov@openvz.org> wrote:

> Andrew Morton wrote:
>  >
>  > (switched to email.  Please respond via emailed reply-to-all, not via the
>  > bugzilla web interface).
>  >
>  > On Thu, 28 Jul 2011 12:41:03 GMT
>  > bugzilla-daemon@bugzilla.kernel.org wrote:
>  >
>  >> https://bugzilla.kernel.org/show_bug.cgi?id=40262
>  >
>  > Two people are reporting this - there are some additional details in
>  > bugzilla.
>  >
>  > We seem to be going around in circles here.
>  >
>  > I'll ask Rafael and Maciej to track this as a regression :(
>  >
> 
> >>
> >> issue occurs in new kernel 3.0.
> >> does not occurs in 2.6.39.3/2.6.38.8
> >>
> 
> I guess this can be caused by commit v2.6.39-6846-g246e87a "memcg: fix vmscan count in small memcgs"
> (it also tweaked kswapd besides of memcg reclaimer)
> it was fixed in v3.0-5361-g4508378 "memcg: fix get_scan_count() for small targets"
> 
> commit 4508378b9523e22a2a0175d8bf64d932fb10a67d
> Author: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Date:   Tue Jul 26 16:08:24 2011 -0700
> 
>      memcg: fix vmscan count in small memcgs
> 
>      Commit 246e87a93934 ("memcg: fix get_scan_count() for small targets")
>      fixes the memcg/kswapd behavior against small targets and prevent vmscan
>      priority too high.
> 
>      But the implementation is too naive and adds another problem to small
>      memcg.  It always force scan to 32 pages of file/anon and doesn't handle
>      swappiness and other rotate_info.  It makes vmscan to scan anon LRU
>      regardless of swappiness and make reclaim bad.  This patch fixes it by
>      adjusting scanning count with regard to swappiness at el.
> 
>      At a test "cat 1G file under 300M limit." (swappiness=20)
>       before patch
>              scanned_pages_by_limit 360919
>              scanned_anon_pages_by_limit 180469
>              scanned_file_pages_by_limit 180450
>              rotated_pages_by_limit 31
>              rotated_anon_pages_by_limit 25
>              rotated_file_pages_by_limit 6
>              freed_pages_by_limit 180458
>              freed_anon_pages_by_limit 19
>              freed_file_pages_by_limit 180439
>              elapsed_ns_by_limit 429758872
>       after patch
>              scanned_pages_by_limit 180674
>              scanned_anon_pages_by_limit 24
>              scanned_file_pages_by_limit 180650
>              rotated_pages_by_limit 35
>              rotated_anon_pages_by_limit 24
>              rotated_file_pages_by_limit 11
>              freed_pages_by_limit 180634
>              freed_anon_pages_by_limit 0
>              freed_file_pages_by_limit 180634
>              elapsed_ns_by_limit 367119089
>              scanned_pages_by_system 0
> 
>      the numbers of scanning anon are decreased(as expected), and elapsed time
>      reduced. By this patch, small memcgs will work better.
>      (*) Because the amount of file-cache is much bigger than anon,
>          recalaim_stat's rotate-scan counter make scanning files more.
> 

Ah, yes. this patch may be able to fix the probelm...could you try ? 

Thanks,
-Kame

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