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Date: Thu, 05 Apr 2007 08:09:41 +0200
From: Eric Dumazet <dada1@cosmosbay.com>
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To: Nick Piggin <nickpiggin@yahoo.com.au>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Andrew Morton <akpm@linux-foundation.org>,
       Jakub Jelinek <jakub@redhat.com>, Ulrich Drepper <drepper@redhat.com>,
       Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
       Hugh Dickins <hugh@veritas.com>
Subject: Re: missing madvise functionality
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Nick Piggin a écrit :
> Eric Dumazet wrote:
> >> This was not a working patch, just to throw the idea, since the
>> answers I got showed I was not understood.
>>
>> In this case, find_extend_vma() should of course have one struct 
>> vm_area_cache * argument, like find_vma()
>>
>> One single cache on one mm is not scalable. oprofile badly hits it on 
>> a dual cpu config.
> 
> Oh, what sort of workload are you using to show this? The only reason 
> that I
> didn't submit my thread cache patches was that I didn't show a big enough
> improvement.
> 

Database workload, where the user multi threaded app is constantly accessing 
GBytes of data, so L2 cache hit is very small. If you want to oprofile it, 
with say a CPU_CLK_UNHALTED:5000 event, then find_vma() is in the top 5.

Each time oprofile has an NMI, it calls find_vma(EIP/RIP) and blows out the 
target process cache (usually plugged on the data vma containing user land 
futexes). Event with private futexes, it will probably be plugged on the brk() 
vma.