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Subject: Re: 2.6.38 sbrk regression
From: raz ben yehuda <raziebe@gmail.com>
To: Andrea Arcangeli <aarcange@redhat.com>,
        lkml <linux-kernel@vger.kernel.org>
Cc: riel@redhat.com, kosaki.motohiro@jp.fujitsu.com, akpm@linux-foundation.org,
        Mel Gorman <mel@csn.ul.ie>
In-Reply-To: <20110413125146.GR29444@random.random>
References: <1302692638.15225.14.camel@raz.scalemp.com>
	 <20110413125146.GR29444@random.random>
Content-Type: text/plain; charset="UTF-8"
Date: Wed, 13 Apr 2011 17:06:19 +0300
Message-ID: <1302703579.17536.1.camel@raz.scalemp.com>
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ok, managed to build 38-rc3 ( keep forgetting make mrproper ).
problem is still there:

------------------------------------------------------------------------------------------------------------
 Test        Test        Elapsed  Iteration    Iteration
Operation
Number       Name      Time (sec)   Count   Rate (loops/sec)    Rate
(ops/sec)
------------------------------------------------------------------------------------------------------------
     1 page_test            5.02        361   71.91235       122251.00
System Allocations & Pages/second
------------------------------------------------------------------------------------------------------------


while in 2.6.37 rate is 171000.
ftrace is no good here as it changes the results to greatly.
any idea ?


On Wed, 2011-04-13 at 14:51 +0200, Andrea Arcangeli wrote:
> Hi,
> 
> CC'ing Mel.
> 
> On Wed, Apr 13, 2011 at 02:03:58PM +0300, raz ben yehuda wrote:
> > Andrea Hello
> > 
> > I am running the AIM benchmark suite looking for regressions in 2.6.38.
> > The test page_test tests sbrk(). 2.6.38 is 13% less than 2.6.27 and 11%
> > less than 2.6.37.
> > The regression starts somewhere in the THP patch:  
> > SHA1 4e9f64c42d0ba5eb0c78569435ada4c224332ce4  to
> > SHA1 152c9ccb75548c027fa3103efa4fa4e19a345449 . 
> > 
> > I cannot git bisect it any more as the kernel won't compile.
> > Even if i disable THP in the kernel I still get a regression. 
> > I performed the benchmark on Xeon blade 3GHZ. But it also happens in
> > other types of machines.
> > 
> > 2.6.38
> > Apr 13 13:31:16 2011 AIM Independent Resource Benchmark - Suite IX 5120
> > page_test 30010 85.0716       144621.79 System Allocations &Pages/second
> > 
> > 2.6.37
> > Apr 13 13:44:39 2011 AIM Independent Resource Benchmark - Suite IX 5120
> > page_test 5020 100.797       171354.58 System Allocations & Pages/second
> > 
> > I am going to profile it hopefully I will have more information.
> 
> The compaction kswapd caused regressions in fs benchs like specsfs,
> it's fixed in 2.6.39-rc. Obviously it will go away if you set
> CONFIG_COMPACTION=n, but 2.6.39-rc should work best with COMPACTION=y
> too. Could you try latest 2.6.39 git?
> 
> Also please make sure CONFIG_SLUB=n and CONFIG_SLAB=y. We must fix
> SLUB so it stops allocating with GFP_KERNEL in the higher order alloc,
> I think it should only do a quick check of the buddy with
> GFP_ATOMIC. The pageblock types are the thing that prevents
> fragmentation, no need of special logic for that in slub. It's
> unlikely that for short lived allocations succeeding the high order
> allocation provides enough speedup to the code using the memory, in
> order to at least break even with the cost of compacting the memory to
> succeed the allocation.


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