linux-kernel - Re: missing madvise functionality

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Date:	Wed, 04 Apr 2007 18:55:18 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Eric Dumazet <dada1@...mosbay.com>,
	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

Peter Zijlstra wrote:
> On Wed, 2007-04-04 at 12:22 +1000, Nick Piggin wrote:
> 
>>Eric Dumazet wrote:
> 
> 
>>>I do think such workloads might benefit from a vma_cache not shared by 
>>>all threads but private to each thread. A sequence could invalidate the 
>>>cache(s).
>>>
>>>ie instead of a mm->mmap_cache, having a mm->sequence, and each thread 
>>>having a current->mmap_cache and current->mm_sequence
>>
>>I have a patchset to do exactly this, btw.
> 
> 
> /me too
> 
> However, I decided against pushing it because when it does happen that a
> task is not involved with a vma lookup for longer than it takes the seq
> count to wrap we have a stale pointer...
> 
> We could go and walk the tasks once in a while to reset the pointer, but
> it all got a tad involved.

Well here is my core patch (against I think 2.6.16 + a set of vma cache
cleanups and abstractions). I didn't think the wrapping aspect was
terribly involved.

-- 
SUSE Labs, Novell Inc.

View attachment "mm-thread-vma-cache.patch" of type "text/plain" (4390 bytes)