linux-ext4 - Re: [PATCH] mm: Improve cmtime update on shared writable mmaps

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Message-ID: <20111102073812.GB17580@infradead.org>
Date:	Wed, 2 Nov 2011 03:38:12 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Jan Kara <jack@...e.cz>, Andreas Dilger <adilger@...ger.ca>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] mm: Improve cmtime update on shared writable mmaps

On Tue, Nov 01, 2011 at 04:02:24PM -0700, Andy Lutomirski wrote:
> Hmm.  Isn't it permitted to at least read from an fs while holding the
> page lock?  I thought that the page lock was held for the entire
> duration of a read and at the beginning of writeback.
> 
> I can push this down to the ->writepage implementations or to the
> clear_page_dirty_for_io callers, but that will result in a bigger
> patch.

Besides the current way that seems to be the only reasonable place to
do it.  Pushing it into ->writepage also has the benefit that
filesystems could piggy back the ctime update onto the transaction that
updates the extent tree.

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