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From: Christoph Hellwig <hch@lst.de>
To: Dave Chinner <david@fromorbit.com>
Cc: Amir Goldstein <amir73il@gmail.com>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [QUESTION] Long read latencies on mixed rw buffered IO
Date: Mon, 25 Mar 2019 07:51:55 +0100	[thread overview]
Message-ID: <20190325065155.GA21259@lst.de> (raw)
In-Reply-To: <20190325001044.GA23020@dastard>

On Mon, Mar 25, 2019 at 11:10:44AM +1100, Dave Chinner wrote:
> That's one part of it. The other is POSIX atomic write semantics.
> 
> https://pubs.opengroup.org/onlinepubs/009695399/functions/read.html
> 
> "I/O is intended to be atomic to ordinary files and pipes and FIFOs.
> Atomic means that all the bytes from a single operation that started
> out together end up together, without interleaving from other I/O
> operations."
> 
> i.e. that independent read()s should see a write() as a single
> atomic change. hence if you do a read() concurrently with a write(),
> the read should either run to completion before the write, or the
> write run to completion before the read().
> 
> XFS is the only linux filesystem that provides this behaviour.

I don't think that is entirely true.  ocfs2 and gfs2 also took
a cluster wide shared lock in read last time I looked, and of
course we do the right thing when using DAX for all supported
file systems.

  reply	other threads:[~2019-03-25  6:52 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-24 18:18 [QUESTION] Long read latencies on mixed rw buffered IO Amir Goldstein
2019-03-25  0:10 ` Dave Chinner
2019-03-25  6:51   ` Christoph Hellwig [this message]
2019-03-25  6:55     ` Amir Goldstein
2019-03-25  7:49   ` Amir Goldstein
2019-03-25 15:47     ` Darrick J. Wong
2019-03-25 16:41       ` Matthew Wilcox
2019-03-25 17:30         ` Amir Goldstein
2019-03-25 18:22           ` Matthew Wilcox
2019-03-25 19:18             ` Amir Goldstein
2019-03-25 19:40               ` Matthew Wilcox
2019-03-25 19:57                 ` Amir Goldstein
2019-03-25 23:48                   ` Dave Chinner
2019-03-26  3:44                     ` Amir Goldstein
2019-03-27  1:29                       ` Dave Chinner
2019-03-25 17:56       ` Amir Goldstein
2019-03-25 18:02         ` Christoph Hellwig
2019-03-25 18:44           ` Amir Goldstein
2019-03-25 23:43     ` Dave Chinner
2019-03-26  4:36       ` Amir Goldstein
2025-06-20 13:46   ` [PATCH] xfs: Remove i_rwsem lock in buffered read Jinliang Zheng

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