linux-kernel - Re: missing madvise functionality

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Message-ID: <461494FE.1040403@redhat.com>
Date:	Wed, 04 Apr 2007 23:19:42 -0700
From:	Ulrich Drepper <drepper@...hat.com>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Nick Piggin <nickpiggin@...oo.com.au>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jakub Jelinek <jakub@...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

Eric Dumazet wrote:
> 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.

We did have a workload with lots of Java and databases at some point
when many VMAs were the issue.  I brought this up here one, maybe two
years ago and I think Blaisorblade went on and looked into avoiding VMA
splits by having mprotect() not split VMAs and instead store the flags
in the page table somewhere.  I don't remember the details.

Nothing came out of this but if this is possible it would be yet another
way to avoid mmap_sem locking, right?

-- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖

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