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Subject: Re: 2.6.38 page_test regression
From: raz ben yehuda <raziebe@gmail.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: lkml <linux-kernel@vger.kernel.org>, riel@redhat.com,
        kosaki.motohiro@jp.fujitsu.com, akpm@linux-foundation.org,
        Mel Gorman <mel@csn.ul.ie>
In-Reply-To: <20110414150925.GD15707@random.random>
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	 <20110413172127.GB5734@random.random>
	 <1302781754.5098.13.camel@raz.scalemp.com>
	 <20110414150925.GD15707@random.random>
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Date: Thu, 14 Apr 2011 23:07:23 +0300
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bah. Mel is correct. I did mean page_test  ( in my defense it is in the
msg ).
Here some more information:
1. I manage to lower the regression to 2 sha1's:
    	32dba98e085f8b2b4345887df9abf5e0e93bfc12 to
71e3aac0724ffe8918992d76acfe3aad7d8724a5. 
	though I had to remark wait_split_huge_page for the sake of
compilation. up to 32dba98e085f8b2b4345887df9abf5e0e93bfc12 there is no
regression.

2. I booted 2.6.37-rc5 you gave me. same regression is there. 

raz


On Thu, 2011-04-14 at 17:09 +0200, Andrea Arcangeli wrote:
> On Thu, Apr 14, 2011 at 02:49:14PM +0300, raz ben yehuda wrote:
> > Hey Andrea
> > Me again. I managed to ftrace ( function graph ) the two kernels. I used
> > 2.6.37 and 2.6.39-rc3. The bellow is example for sys_brk calls traces
> > from each kernel. As you can see, there is no "single smoking gun"
> > here. 
> > 
> > The vm functions durations increased as a whole.
> > I repeated the tests from sha1 4e9f64c42d0ba5eb0c78569435ada4c224332ce4
> > compared to sha1 152c9ccb75548c027fa3103efa4fa4e19a345449  and it is
> > consistent. ~13% performance decrease.
> > 
> 
> > Can you see any relation to thp that might causes this degradation ?
> 
> With compaction and THP off I don't see how it could change
> anything.
> 
> But can you try the THP-33 tag of my aa.git tree, that was based on
> 2.3.37-rc5 so it'll rule out the whole THP patchset if it doesn't
> regress compared to 2.6.37-rc5 vanilla.
> 
> git clone --reference linux-2.6 git://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git
> git checkout THP-33
> 
> Thanks,
> Andrea


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