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From: Matthew Bobrowski <mbobrowski@mbobrowski.org>
To: Jan Kara <jack@suse.cz>
Cc: tytso@mit.edu, adilger.kernel@dilger.ca,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	hch@infradead.org, david@fromorbit.com, darrick.wong@oracle.com
Subject: Re: [PATCH v4 4/8] ext4: introduce direct I/O read path using iomap infrastructure
Date: Wed, 9 Oct 2019 21:55:09 +1100
Message-ID: <20191009105507.GF14749@poseidon.bobrowski.net> (raw)
In-Reply-To: <20191008105207.GG5078@quack2.suse.cz>

On Tue, Oct 08, 2019 at 12:52:07PM +0200, Jan Kara wrote:
> On Thu 03-10-19 21:34:00, Matthew Bobrowski wrote:
> > This patch introduces a new direct I/O read path that makes use of the
> > iomap infrastructure.
> > 
> > The new function ext4_dio_read_iter() is responsible for calling into
> > the iomap infrastructure via iomap_dio_rw(). If the read operation
> > being performed on the inode does not pass the preliminary checks
> > performed within ext4_dio_supported(), then we simply fallback to
> > buffered I/O in order to fulfil the request.
> > 
> > Existing direct I/O read buffer_head code has been removed as it's now
> > redundant.
> > 
> > Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
> 
> The patch looks good to me. Just one small nit below. With that fixed, you
> can add:
> 
> Reviewed-by: Jan Kara <jack@suse.cz>

Cool, I'll fix it!

> > +	/*
> > +	 * Get exclusion from truncate and other inode operations.
> > +	 */
> > +	if (!inode_trylock_shared(inode)) {
> > +		if (iocb->ki_flags & IOCB_NOWAIT)
> > +			return -EAGAIN;
> > +		inode_lock_shared(inode);
> > +	}
> 
> I've noticed here you actually introduce new trylock pattern - previously
> we had unconditional inode_lock_shared() in ext4_direct_IO_read(). So the
> cleanest would be to just use unconditional inode_lock_shared() here and
> then fixup IOCB_NOWAIT handling (I agree that was missing in the original
> code) in a separate patch.

Right, so I will just have an unconditional call to
inode_lock_shared() and in the patch that follows I will fix it up to
apply the new pattern.

> And the pattern should rather look like:
>
> 	if (iocb->ki_flags & IOCB_NOWAIT) {
> 		if (!inode_trylock_shared(inode))
> 			return -EAGAIN;
> 	} else {
> 		inode_lock_shared(inode);
> 	}
> 
> to avoid two atomical operations instead of one in the fast path. No need
> to repeat old mistakes when we know better :).

Yes, also agree.

--<M>--

  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-03 11:32 [PATCH v4 0/8] ext4: port direct I/O to " Matthew Bobrowski
2019-10-03 11:33 ` [PATCH v4 1/8] ext4: move out iomap field population into separate helper Matthew Bobrowski
2019-10-08 10:27   ` Jan Kara
2019-10-09  8:57     ` Matthew Bobrowski
2019-10-09 13:06       ` Jan Kara
2019-10-10  5:39         ` Matthew Bobrowski
2019-10-09  6:02   ` Ritesh Harjani
2019-10-09  7:07     ` Christoph Hellwig
2019-10-09  7:50       ` Ritesh Harjani
2019-10-09  9:09         ` Matthew Bobrowski
2019-10-03 11:33 ` [PATCH v4 2/8] ext4: move out IOMAP_WRITE path " Matthew Bobrowski
2019-10-08 10:31   ` Jan Kara
2019-10-09  9:18     ` Matthew Bobrowski
2019-10-09  6:22   ` Ritesh Harjani
2019-10-09  9:31     ` Matthew Bobrowski
2019-10-03 11:33 ` [PATCH v4 3/8] ext4: introduce new callback for IOMAP_REPORT operations Matthew Bobrowski
2019-10-08 10:42   ` Jan Kara
2019-10-09  9:41     ` Matthew Bobrowski
2019-10-09  6:00   ` Ritesh Harjani
2019-10-09 12:08     ` Matthew Bobrowski
2019-10-09 13:14       ` Ritesh Harjani
2019-10-03 11:34 ` [PATCH v4 4/8] ext4: introduce direct I/O read path using iomap infrastructure Matthew Bobrowski
2019-10-08 10:52   ` Jan Kara
2019-10-09 10:55     ` Matthew Bobrowski [this message]
2019-10-09  6:39   ` Ritesh Harjani
2019-10-03 11:34 ` [PATCH v4 5/8] ext4: move inode extension/truncate code out from ->iomap_end() callback Matthew Bobrowski
2019-10-08 11:25   ` Jan Kara
2019-10-09 10:18     ` Matthew Bobrowski
2019-10-09 12:51       ` Jan Kara
2019-10-10  5:44         ` Matthew Bobrowski
2019-10-09  6:27   ` Ritesh Harjani
2019-10-09 10:20     ` Matthew Bobrowski
2019-10-03 11:34 ` [PATCH v4 6/8] ext4: move inode extension checks out from ext4_iomap_alloc() Matthew Bobrowski
2019-10-08 11:27   ` Jan Kara
2019-10-09 10:21     ` Matthew Bobrowski
2019-10-09  6:30   ` Ritesh Harjani
2019-10-09 10:39     ` Matthew Bobrowski
2019-10-03 11:34 ` [PATCH v4 7/8] ext4: reorder map.m_flags checks in ext4_set_iomap() Matthew Bobrowski
2019-10-08 11:30   ` Jan Kara
2019-10-09 10:42     ` Matthew Bobrowski
2019-10-09  6:35   ` Ritesh Harjani
2019-10-09 10:43     ` Matthew Bobrowski
2019-10-03 11:35 ` [PATCH v4 8/8] ext4: introduce direct I/O write path using iomap infrastructure Matthew Bobrowski
2019-10-08 15:12   ` Jan Kara
2019-10-09  7:11     ` Christoph Hellwig
2019-10-09 13:41       ` Jan Kara
2019-10-09 11:53     ` Matthew Bobrowski

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