linux-kernel - Re: page_mkwrite caller is racy?

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Message-ID: <Pine.LNX.4.64.0701301456250.6541@hermes-1.csi.cam.ac.uk>
Date:	Tue, 30 Jan 2007 14:58:50 +0000 (GMT)
From:	Anton Altaparmakov <aia21@....ac.uk>
To:	Mark Fasheh <mark.fasheh@...cle.com>
cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Hugh Dickins <hugh@...itas.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux Memory Management <linux-mm@...ck.org>,
	David Howells <dhowells@...hat.com>,
	Andrew Morton <akpm@...l.org>
Subject: Re: page_mkwrite caller is racy?

On Mon, 29 Jan 2007, Mark Fasheh wrote:
> On Tue, Jan 30, 2007 at 12:14:24PM +1100, Nick Piggin wrote:
> > This is another discussion, but do we want the page locked here? Or
> > are the filesystems happy to exclude truncate themselves?
> 
> No page lock please. Generally, Ocfs2 wants to order cluster locks outside
> of page locks. Also, the sparse b-tree support I'm working on right now will
> need to be able to allocate in ->page_mkwrite() which would become very
> nasty if we came in with the page lock - aside from the additional cluster
> locks taken, ocfs2 will want to zero some adjacent pages (because we support
> atomic allocation up to 1 meg).

Ditto for NTFS.  I will need to lock pages on both sides of the page for 
large volume cluster sizes thus I will have to drop the page lock if it is 
already taken so it might as well not be...  Although I do not feel 
strongly about it.  If the page is locked I will just drop the lock and 
then take it again.  If possible to not have the page locked that would 
make my code a little easier/more efficient I expect...

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer, http://www.linux-ntfs.org/
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