Re: mm-more-likely-reclaim-madv_sequential-mappings.patch

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 16 Oct 2008 15:22:15 +0900 (JST) KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

> > >                          2.6.27    mmotm-1010
> > >    ==============================================================
> > >    mm_sync_madv_cp       6:14      6:02         (min:sec)
> > >    dbench throughput     12.1507   14.6273      (MB/s)
> > >    dbench latency        33046     21779        (ms)
> > > 
> > > 
> > >    So, throughput improvement is relativily a bit, but latency improvement is much.
> > >    Then, I think the patch can improve "larege file copy (e.g. backup operation)
> > >    attacks desktop latency" problem.
> > > 
> > > Any comments?
> > > 
> > 
> > Sounds good.
> > 
> > But how do we know that it was this particular patch which improved the
> > latency performance?
> 
> In my concern,
> 
> dbench's pages are touched multiple times, but copy's pages are touched only twice.
> Then, on 2.6.27, copy's page transit to inactive -> active -> inactive -> free.
> it decrease latency meaninglessly.
> 
> IOW, 2.6.27 model
> 
> 1. shrink_inactive_lsit() promote copy's page to active (it touched twice (readahead + memcpy))
> 2. shrink_active_list() demote dbench's page
> 3. shrink_inactive_list() promote dbench's page (because it is touched multiple times)
> 4. shrink_active_list() demote copy's page
> 5. shrink_inactive_list() free copy's page
> 
> 
> mmotm mode,
> 
> 1, shrink_inactive_list() free copy's page.
> 2. end!

OK.  But my concern is that perhaps the above latency improvement was
caused by one of the many other MM patches in mmotm.

Reverting mm-more-likely-reclaim-madv_sequential-mappings.patch from
mmotm and rerunning the tests would be the way to determine this. 
(hint :) - thanks).


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