From: Matthew Wilcox <willy@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>,
jlayton@redhat.com, dchinner@redhat.com,
linux-fsdevel@vger.kernel.org, linux-cachefs@redhat.com
Subject: Re: Problems doing DIO to netfs cache on XFS from Ceph
Date: Thu, 3 Dec 2020 15:50:43 +0000 [thread overview]
Message-ID: <20201203155043.GI11935@casper.infradead.org> (raw)
In-Reply-To: <914680.1607004656@warthog.procyon.org.uk>
On Thu, Dec 03, 2020 at 02:10:56PM +0000, David Howells wrote:
> Note that I'm only doing async DIO reads and writes, so I was a bit surprised
> that XFS is doing a writeback at all - but I guess that IOCB_DIRECT is
> actually just a hint and the filesystem can turn it into buffered I/O if it
> wants.
That's almost the exact opposite of what is going on. XFS sees that
you're going to do an O_DIRECT read, so it writes back the dirty memory
that's currently in the page cache so that your read doesn't read stale
data from disk.
next prev parent reply other threads:[~2020-12-03 15:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-03 14:10 Problems doing DIO to netfs cache on XFS from Ceph David Howells
2020-12-03 15:50 ` Matthew Wilcox [this message]
2020-12-03 16:04 ` David Howells
2020-12-03 22:12 ` Dave Chinner
2020-12-03 23:05 ` Matthew Wilcox
2020-12-04 1:50 ` Yafang Shao
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