From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Matthew Bobrowski <mbobrowski@mbobrowski.org>,
Ritesh Harjani <riteshh@linux.ibm.com>,
tytso@mit.edu, jack@suse.cz, adilger.kernel@dilger.ca,
linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
hch@infradead.org, aneesh.kumar@linux.ibm.com
Subject: Re: [PATCH 0/5] ext4: direct IO via iomap infrastructure
Date: Sat, 24 Aug 2019 16:04:27 -0700 [thread overview]
Message-ID: <20190824230427.GA32012@infradead.org> (raw)
In-Reply-To: <20190824035554.GA1037502@magnolia>
On Fri, Aug 23, 2019 at 08:55:54PM -0700, Darrick J. Wong wrote:
> I'm probably misunderstanding the ext4 extent cache horribly, but I keep
> wondering why any of this is necessary -- why can't ext4 track the
> unwritten status in the extent records directly? And why is there all
> this strange "can merge" logic? If you need to convert blocks X to Y
> to written state because a write to those blocks completed, isn't that
> just manipulation of a bunch of incore records? And can't you just seek
> back and forth in the extent cache to look for adjacent records to merge
> with? <confuseD>
Same here. I'm not an ext4 expert, but here is what we do in XFS, which
hopefully works in some form for ext4 a well:
- when starting a direct I/O we allocate any needed blocks and do so
as unwritten extent. The extent tree code will merge them in
whatever way that seems suitable
- if the IOMAP_DIO_UNWRITTEN is set on the iomap at ->end_io time we
call a function that walks the whole range covered by the ioend,
and convert any unwritten extent to a normal written extent. Any
splitting and merging will be done as needed by the low-level
extent tree code
- this also means we don't need the xfs_ioen structure (which ext4)
copied from for direct I/O at all (we used to have it initially,
though including the time when ext4 copied this code).
- we don't need the equivalent to the ext4_unwritten_wait call in
ext4_file_write_iter because we serialize any non-aligned I/O
instead of trying to optimize for weird corner cases
> (I'd really prefer not to go adding private fields all over the
> place...)
Agreed.
next prev parent reply other threads:[~2019-08-24 23:04 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-12 12:52 [PATCH 0/5] ext4: direct IO via iomap infrastructure Matthew Bobrowski
2019-08-12 12:52 ` [PATCH 1/5] ext4: introduce direct IO read code path using " Matthew Bobrowski
2019-08-12 17:18 ` Christoph Hellwig
2019-08-12 20:17 ` Matthew Wilcox
2019-08-13 10:45 ` Matthew Bobrowski
2019-08-12 12:52 ` [PATCH 2/5] ext4: move inode extension/truncate code out from ext4_iomap_end() Matthew Bobrowski
2019-08-12 17:18 ` Christoph Hellwig
2019-08-13 10:46 ` Matthew Bobrowski
2019-08-28 19:59 ` Jan Kara
2019-08-28 21:54 ` Matthew Bobrowski
2019-08-29 8:18 ` Jan Kara
2019-08-12 12:53 ` [PATCH 3/5] iomap: modify ->end_io() calling convention Matthew Bobrowski
2019-08-12 17:18 ` Christoph Hellwig
2019-08-13 10:43 ` Matthew Bobrowski
2019-08-12 12:53 ` [PATCH 4/5] ext4: introduce direct IO write code path using iomap infrastructure Matthew Bobrowski
2019-08-12 17:04 ` RITESH HARJANI
2019-08-13 12:58 ` Matthew Bobrowski
2019-08-13 14:35 ` Darrick J. Wong
2019-08-14 9:51 ` Matthew Bobrowski
2019-08-12 17:34 ` Christoph Hellwig
2019-08-13 10:45 ` Matthew Bobrowski
2019-08-28 20:26 ` Jan Kara
2019-08-28 22:32 ` Dave Chinner
2019-08-29 8:03 ` Jan Kara
2019-08-29 11:47 ` Matthew Bobrowski
2019-08-29 11:45 ` Matthew Bobrowski
2019-08-29 12:38 ` Jan Kara
2019-08-12 12:53 ` [PATCH 5/5] ext4: clean up redundant buffer_head direct IO code Matthew Bobrowski
2019-08-12 17:31 ` [PATCH 0/5] ext4: direct IO via iomap infrastructure RITESH HARJANI
2019-08-13 11:10 ` Matthew Bobrowski
2019-08-13 12:27 ` RITESH HARJANI
2019-08-14 9:48 ` Matthew Bobrowski
2019-08-14 11:58 ` RITESH HARJANI
2019-08-21 13:14 ` Matthew Bobrowski
2019-08-22 12:00 ` Matthew Bobrowski
2019-08-22 14:11 ` Ritesh Harjani
2019-08-24 3:18 ` Matthew Bobrowski
2019-08-24 3:55 ` Darrick J. Wong
2019-08-24 23:04 ` Christoph Hellwig [this message]
2019-08-27 9:52 ` Matthew Bobrowski
2019-08-28 12:05 ` Matthew Bobrowski
2019-08-28 14:27 ` Theodore Y. Ts'o
2019-08-28 18:02 ` Jan Kara
2019-08-29 6:36 ` Christoph Hellwig
2019-08-29 11:20 ` Matthew Bobrowski
2019-08-29 14:41 ` Christoph Hellwig
2019-08-23 13:43 ` [RFC 1/1] ext4: PoC implementation of option-1 Ritesh Harjani
2019-08-23 13:49 ` Ritesh Harjani
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