linux-kernel - Re: missing madvise functionality

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Date:	Thu, 05 Apr 2007 03:31:24 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Jakub Jelinek <jakub@...hat.com>
CC:	Ulrich Drepper <drepper@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Hugh Dickins <hugh@...itas.com>
Subject: Re: missing madvise functionality

Jakub Jelinek wrote:

> My guess is that all the page zeroing is pretty expensive as well and
> takes significant time, but I haven't profiled it.

With the attached patch (Andrew, I'll change the details around
if you want - I just wanted something to test now), your test
case run time went down considerably.

I modified the test case to only run 1000 loops, so it would run
a bit faster on my system.  I also modified it to use MADV_DONTNEED
to zap the pages, instead of the mmap(PROT_NONE) thing you use.


MADV_DONTNEED, unpatched, 1000 loops

real    0m13.672s
user    0m1.217s
sys     0m45.712s


MADV_DONTNEED, with patch, 1000 loops

real    0m4.169s
user    0m2.033s
sys     0m3.224s


-- 
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.

View attachment "linux-2.6-madv_free.patch" of type "text/x-patch" (11298 bytes)