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

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Message-ID: <20160706070429.GA14067@quack2.suse.cz>
Date:	Wed, 6 Jul 2016 09:04:29 +0200
From:	Jan Kara <jack@...e.cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Jan Kara <jack@...e.cz>, 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 04-07-16 22:43:30, Ted Tso wrote:
> 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....

Yes, I completely agree.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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