linux-kernel - Re: [patch 2/3] MAP_NOZERO

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Message-ID: <Pine.LNX.4.64.0706271111040.32731@alien.or.mcafeemobile.com>
Date:	Wed, 27 Jun 2007 11:13:52 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Hugh Dickins <hugh@...itas.com>
cc:	Ulrich Drepper <drepper@...il.com>, blaisorblade@...oo.it,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch 2/3] MAP_NOZERO - implement sys_brk2()

On Wed, 27 Jun 2007, Hugh Dickins wrote:

> In honesty, I should add that I dislike and distrust Davide's
> MAP_NOZERO very much indeed!  Would much rather leave my cpus
> spending a little time in clear_page().  A uid in struct page
> (though I'm sure we could find somewhere to tuck it away) -
> the horror, the horror!  But I've so far failed to find a killer
> argument against it, and am hoping for someone else to do so.

Little time? Please, do not trust me. Start oprofile and run a kernel 
build. Look, I'm not even talking about som micro benchmark explicitly 
built to exploit the thing. A kernel build.
You will find clear_page to be the *1st* kernel entry after cc1 and as.
That is bad for two reasons. The time it spends in there, and the cache it 
blows.



- Davide


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