linux-ext4 - Re: [PATCH 1/4] ext4: Fix deadlock during page writeback

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Message-ID: <20160705024330.GB15193@thunk.org>
Date:	Mon, 4 Jul 2016 22:43:30 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org, Eryu Guan <eguan@...hat.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH 1/4] ext4: Fix deadlock during page writeback

On Mon, Jul 04, 2016 at 05:47:09PM +0200, Jan Kara wrote:
> > Good point that the block device is plugged.  Ultimately I suspect the
> > way to fix the scalability problem will be move to dioread nolock as
> > the default, and use separate transaction to map the blocks using the
> > uninitialized flags, and then do a separate transaction to convert
> > them afterwards.
> 
> This is what already happens currently - we only reserve a handle for
> conversion during writeback but that reservation fluently moves between
> running transactions until a point where the reserved handle is started -
> then the handle is pinned to the currently running transaction - and this
> happens only in the completion handler after IO is completed.

Yes, but dioread_nolock only works with block size == page size.  What
we need to do is to make it work for all block sizes, then make
dioread_nolock the default, and then remove the old direct I/O write
path....


					- Ted
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