linux-ext4 - Re: Delayed allocation and page_lock vs transaction start ordering

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Date:	Fri, 18 Apr 2008 12:54:47 -0600
From:	Andreas Dilger <adilger@....com>
To:	Jan Kara <jack@...e.cz>
Cc:	Mingming Cao <cmm@...ibm.com>, linux-ext4@...r.kernel.org,
	sandeen@...hat.com
Subject: Re: Delayed allocation and page_lock vs transaction start ordering

On Apr 16, 2008  11:38 +0200, Jan Kara wrote:
> On Tue 15-04-08 11:08:52, Mingming Cao wrote:
> > I guess this reserve locking ordering allows support writepages() for
> > ext3/4? What other the benefits?
>
>   Yes, that is one advantage. The other one (which I care about the most)
> is that transaction commit code can take page_lock in the new locking order
> which is necessary for the new ordered mode rewrite.

My understanding is that the main reason for the ordered mode rewrite is
specifically to allow delalloc to still support ordered mode semantics.
If the lock ordering is changed, and the jbd ordered mode is changed, but
we don't support that with delalloc then we will have made a lot of changes
(and likely introduced some bugs) with little benefit.

My apologies in advance if I misunderstand, and delalloc will be supported
with these changes.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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