linux-kernel - Re: [patch] agp: don't lock pages

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Date:	Thu, 26 Jul 2007 04:07:04 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Dave Airlie <airlied@...il.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	magnade@...il.com, davej@...emonkey.org.uk
Subject: Re: [patch] agp: don't lock pages

On Thu, Jul 26, 2007 at 11:44:22AM +1000, Dave Airlie wrote:
> >
> >Yeah I had a bit of a look around, and it seems OK (but would
> >appreciate an ack from someone who knows the code).
> >
> >These pages will never get seen by page reclaim, so we're OK
> >there. There is a get_page before the SetPageLocked and a put_page
> >right before the unlock_page, so refcounting should not be broken
> >if it wasn't already: note that the lock_page doesn't pin a
> >reference on a page in general -- we can use it as such for pagecache
> >(although it isn't very clean), because the lock pins the page in
> >pagecache and the pagecache holds a ref.
> >
> >Anyway, if Dave or David can take a look, that would be appreciated.
> >We'll need this for 2.6.23.
> 
> I talked with Ben earlier and I can't see anything inherently wrong
> with removing the lock_page, I assume it was put there to stop things
> getting swapped but if the get/put does that then I'd be happy to
> remove it.

Well it is prevented from being swapped out because it never gets
put on swapout lists, but the get/put certainly doesn't hurt :)
 

> I'm just a bit confused how this didn't get picked up in -mm at all.

Beats me. It was in there for nearly 5 months. Mustn't have been
tested or reported.
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