linux-kernel - Re: missing madvise functionality

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Date:	Thu, 05 Apr 2007 08:09:41 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jakub Jelinek <jakub@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Rik van Riel <riel@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Hugh Dickins <hugh@...itas.com>
Subject: Re: missing madvise functionality

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.

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