linux-kernel - Re: missing madvise functionality

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Date:	Wed, 4 Apr 2007 13:56:18 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Hugh Dickins <hugh@...itas.com>, Jakub Jelinek <jakub@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: missing madvise functionality

On Wed, 04 Apr 2007 14:08:47 -0400
Rik van Riel <riel@...hat.com> wrote:

> Andrew Morton wrote:
> 
> > There are other ways of doing it - I guess we could use a new page flag to
> > indicate that this is one-of-those-pages, and add new code to handle it in
> > all the right places.
> 
> That's what I did.  I'm currently working on the
> zap_page_range() side of things.

Let's try to avoid consuming another page flag if poss, please.  Perhaps
use PAGE_MAPPING_ANON's neighbouring bit?

> > One thing which we haven't sorted out with all this stuff: once the
> > application has marked an address range (and some pages) as
> > whatever-were-going-call-this-feature, how does the application undo that
> > change? 
> 
> It doesn't have to do anything.  Just access the page and the
> MMU will mark it dirty/accessed and the VM will not reclaim
> it.

um, OK.  I suspect it would be good to clear the page's
PageWhateverWereGoingToCallThisThing() state when this happens.  Otherwise
when the page gets clean again (ie: added to swapcache then written out)
then it will look awfully similar to one of these new types of pages and
things might get confusing.  We'll see.

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