linux-ext4 - Re: [PATCH-v4 2/7] vfs: add support for a lazytime mount option

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Message-ID: <20141128053656.GI14091@thunk.org>
Date:	Fri, 28 Nov 2014 00:36:56 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	Linux Filesystem Development List <linux-fsdevel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Linux btrfs Developers List <linux-btrfs@...r.kernel.org>,
	XFS Developers <xfs@....sgi.com>
Subject: Re: [PATCH-v4 2/7] vfs: add support for a lazytime mount option

On Thu, Nov 27, 2014 at 06:00:16PM -0500, Theodore Ts'o wrote:
> Well.... it's not quite enough.  The problem is that for ext3 and
> ext4, the actual work of writing the inode happens in dirty_inode(),
> not in write_inode().  Which means we need to do something like this.
> 
> I'm not entirely sure whether or not this is too ugly to live;
> personally, I think my hack of handling this in update_time() might be
> preferable....

.... and this doesn't work because it breaks ext3/ext4's transaction
handling, since the writeback thread could be racing against some
transactional update of the inode.  So I don't see a way of making the
queue_io / move_expired_inodes approach to the 24 hour time being
tractable.

So the alternatives that I can see at this point is either give up on
the 24 hour timeout, or we fall back to handling this in
update_time().

					- Ted
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