From: Goldwyn Rodrigues <rgoldwyn@suse.de>
To: Matthew Wilcox <willy@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>,
linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org,
fdmanana@gmail.com, dsterba@suse.cz, david@fromorbit.com,
darrick.wong@oracle.com, cluster-devel@redhat.com,
linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org
Subject: Re: always fall back to buffered I/O after invalidation failures, was: Re: [PATCH 2/6] iomap: IOMAP_DIO_RWF_NO_STALE_PAGECACHE return if page invalidation fails
Date: Tue, 7 Jul 2020 08:49:52 -0500 [thread overview]
Message-ID: <20200707134952.3niqhxngwh3gus54@fiona> (raw)
In-Reply-To: <20200707125705.GK25523@casper.infradead.org>
On 13:57 07/07, Matthew Wilcox wrote:
> On Tue, Jul 07, 2020 at 07:43:46AM -0500, Goldwyn Rodrigues wrote:
> > On 9:53 01/07, Christoph Hellwig wrote:
> > > On Mon, Jun 29, 2020 at 02:23:49PM -0500, Goldwyn Rodrigues wrote:
> > > > From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > > >
> > > > For direct I/O, add the flag IOMAP_DIO_RWF_NO_STALE_PAGECACHE to indicate
> > > > that if the page invalidation fails, return back control to the
> > > > filesystem so it may fallback to buffered mode.
> > > >
> > > > Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > >
> > > I'd like to start a discussion of this shouldn't really be the
> > > default behavior. If we have page cache that can't be invalidated it
> > > actually makes a whole lot of sense to not do direct I/O, avoid the
> > > warnings, etc.
> > >
> > > Adding all the relevant lists.
> >
> > Since no one responded so far, let me see if I can stir the cauldron :)
> >
> > What error should be returned in case of such an error? I think the
>
> Christoph's message is ambiguous. I don't know if he means "fail the
> I/O with an error" or "satisfy the I/O through the page cache". I'm
> strongly in favour of the latter. Indeed, I'm in favour of not invalidating
> the page cache at all for direct I/O. For reads, I think the page cache
> should be used to satisfy any portion of the read which is currently
That indeed would make reads faster. How about if the pages are dirty
during DIO reads?
Should a direct I/O read be responsible for making sure that the dirty
pages are written back. Technically direct I/O reads is that we are
reading from the device.
> cached. For writes, I think we should write into the page cache pages
> which currently exist, and then force those pages to be written back,
> but left in cache.
Yes, that makes sense.
If this is implemented, what would be the difference between O_DIRECT
and O_DSYNC, if any?
--
Goldwyn
next prev parent reply other threads:[~2020-07-07 13:49 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-29 19:23 [PATCH 0/6 v10] btrfs direct-io using iomap Goldwyn Rodrigues
2020-06-29 19:23 ` [PATCH 1/6] iomap: Convert wait_for_completion to flags Goldwyn Rodrigues
2020-06-29 23:03 ` David Sterba
2020-06-30 16:35 ` David Sterba
2020-07-01 7:34 ` Johannes Thumshirn
2020-07-01 7:50 ` Christoph Hellwig
2020-06-29 19:23 ` [PATCH 2/6] iomap: IOMAP_DIO_RWF_NO_STALE_PAGECACHE return if page invalidation fails Goldwyn Rodrigues
2020-07-01 7:53 ` always fall back to buffered I/O after invalidation failures, was: " Christoph Hellwig
2020-07-07 12:43 ` Goldwyn Rodrigues
2020-07-07 12:57 ` Matthew Wilcox
2020-07-07 13:00 ` Christoph Hellwig
2020-07-08 6:51 ` Dave Chinner
2020-07-08 13:54 ` Matthew Wilcox
2020-07-08 16:54 ` Christoph Hellwig
2020-07-08 17:11 ` Matthew Wilcox
2020-07-09 8:26 ` [Cluster-devel] " Steven Whitehouse
2020-07-09 2:25 ` Dave Chinner
2020-07-09 16:09 ` Darrick J. Wong
2020-07-09 17:05 ` Matthew Wilcox
2020-07-09 17:10 ` Darrick J. Wong
2020-07-09 22:59 ` Dave Chinner
2020-07-10 16:03 ` Christoph Hellwig
2020-07-12 11:36 ` Avi Kivity
2020-07-07 13:49 ` Goldwyn Rodrigues [this message]
2020-07-07 14:01 ` Darrick J. Wong
2020-07-07 14:30 ` Goldwyn Rodrigues
2020-06-29 19:23 ` [PATCH 3/6] btrfs: switch to iomap_dio_rw() for dio Goldwyn Rodrigues
2020-06-29 19:23 ` [PATCH 4/6] fs: remove dio_end_io() Goldwyn Rodrigues
2020-06-29 19:23 ` [PATCH 5/6] btrfs: remove BTRFS_INODE_READDIO_NEED_LOCK Goldwyn Rodrigues
2020-06-29 19:23 ` [PATCH 6/6] btrfs: split btrfs_direct_IO to read and write part Goldwyn Rodrigues
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