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

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Message-Id: <20080131011227.257b9437.akpm@linux-foundation.org>
Date:	Thu, 31 Jan 2008 01:12:27 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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, 31 Jan 2008 09:44:00 +0100 Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> 
> On Wed, 2008-01-30 at 14:40 -0800, Andrew Morton wrote:
> > On Wed, 30 Jan 2008 18:28:59 +0100
> > Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > 
> > > Implement MADV_WILLNEED for anonymous pages by walking the page tables and
> > > starting asynchonous swap cache reads for all encountered swap pages.
> > 
> > Why cannot this use (a perhaps suitably-modified) make_pages_present()?
> 
> Because make_pages_present() relies on page faults to bring data in and
> will thus wait for all data to be present before returning.
> 
> This solution is async; it will just issue a read for the requested
> pages and moves on.
> 

I of course realise that.  I also realise that swapin_readahead() is
_supposed_ to make the difference moot.

There's something you guys aren't telling us.  Several things, actually. 
Please don't do that.



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? ;)


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