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Date:   Thu, 29 Aug 2019 12:58:58 +0200
From:   Jan Kara <jack@suse.cz>
To:     Dave Chinner <david@fromorbit.com>
Cc:     Joseph Qi <joseph.qi@linux.alibaba.com>,
        Theodore Ts'o <tytso@mit.edu>,
        Andreas Dilger <adilger@dilger.ca>, Jan Kara <jack@suse.cz>,
        linux-ext4@vger.kernel.org
Subject: Re: [PATCH 0/3] Revert parallel dio reads
Message-ID: <20190829105858.GA22939@quack2.suse.cz>
References: <1566871552-60946-1-git-send-email-joseph.qi@linux.alibaba.com>
 <20190827115118.GY7777@dread.disaster.area>
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On Tue 27-08-19 21:51:18, Dave Chinner wrote:
> On Tue, Aug 27, 2019 at 10:05:49AM +0800, Joseph Qi wrote:
> > This patch set is trying to revert parallel dio reads feature at present
> > since it causes significant performance regression in mixed random
> > read/write scenario.
> > 
> > Joseph Qi (3):
> >   Revert "ext4: remove EXT4_STATE_DIOREAD_LOCK flag"
> >   Revert "ext4: fix off-by-one error when writing back pages before dio
> >     read"
> >   Revert "ext4: Allow parallel DIO reads"
> > 
> >  fs/ext4/ext4.h        | 17 +++++++++++++++++
> >  fs/ext4/extents.c     | 19 ++++++++++++++-----
> >  fs/ext4/inode.c       | 47 +++++++++++++++++++++++++++++++----------------
> >  fs/ext4/ioctl.c       |  4 ++++
> >  fs/ext4/move_extent.c |  4 ++++
> >  fs/ext4/super.c       | 12 +++++++-----
> >  6 files changed, 77 insertions(+), 26 deletions(-)
> 
> Before doing this, you might want to have a chat and co-ordinate
> with the folks that are currently trying to port the ext4 direct IO
> code to use the iomap infrastructure:
> 
> https://lore.kernel.org/linux-ext4/20190827095221.GA1568@poseidon.bobrowski.net/T/#t
> 
> That is going to need the shared locking on read and will work just
> fine with shared locking on write, too (it's the code that XFS uses
> for direct IO). So it might be best here if you work towards shared
> locking on the write side rather than just revert the shared locking
> on the read side....

Yeah, after converting ext4 DIO path to iomap infrastructure, using shared
inode lock for all aligned non-extending DIO writes will be easy so I'd
prefer if we didn't have to redo the iomap conversion patches due to these
reverts.

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