linux-ext4 - Re: [PATCH v2 2/3] jbd2: Add extra parameter in start_this

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Message-ID: <20110531222720.GA3867@thunk.org>
Date:	Tue, 31 May 2011 18:27:20 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	Manish Katiyar <mkatiyar@...il.com>, linux-ext4@...r.kernel.org,
	mfasheh@...e.com, jlbec@...lplan.org
Subject: Re: [PATCH v2 2/3] jbd2: Add extra parameter in
 start_this_handle() to control allocation flags.

On Tue, May 31, 2011 at 01:22:53PM +0200, Jan Kara wrote:
> 
> The problem is that with ext4, we need i_mutex in io completion path to
> end page writeback. So we cannot do GFP_KERNEL allocation whenever we hold
> i_mutex because mm might wait in direct reclaim for IO to complete and that
> cannot happen until we release i_mutex. 

OK, maybe I'm being dense, but I'm not seeing it.  I see where we need
i_mutex on the ext4_da_writepages() codepath, but that's never used
for direct reclaim.  Direct reclaim only calls ext4_writepage(), and
that doesn't seem to try to grab i_mutex as near as I can tell.  Am I
missing something?

						- Ted
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