linux-kernel - Re: [PATCH] mm: MADV_WILLNEED implementation for anonymous memory

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Date:	Thu, 31 Jan 2008 10:53:26 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	hugh@...itas.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	npiggin@...e.de, riel@...hat.com, mztabzr@...inter.de,
	mpm@...enic.com
Subject: Re: [PATCH] mm: MADV_WILLNEED implementation for anonymous memory


On Thu, 2008-01-31 at 01:47 -0800, Andrew Morton wrote:
> On Thu, 31 Jan 2008 10:35:18 +0100 Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> > 
> > On Thu, 2008-01-31 at 01:12 -0800, Andrew Morton wrote:
> > 
> > > Implementation-wise: make_pages_present() _can_ be converted to do this. 
> > > But it's a lot of patching, and the result will be a cleaner, faster and
> > > smaller core MM.  Whereas your approach is easy, but adds more code and
> > > leaves the old stuff slow-and-dirty.
> > > 
> > > Guess which approach is preferred? ;)
> > 
> > Ok, I'll look at using make_pages_present().
> 
> Am still curious to know what inspired this change.  What are the use
> cases?  Performance testing results, etc?

Ah, that is Lennarts Pulse Audio thing, he has samples in memory which
might not have been used for a while, and he wants to be able to
pre-fetch those when he suspects they might need to be played. So that
once the audio thread comes along and stuffs them down /dev/dsp its all
nice in memory.

Since its all soft real-time at best he feels its better to do a best
effort at not hitting swap than it is to strain the system with mlock
usage.

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