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From: Goldwyn Rodrigues <>
To: Dave Chinner <>
Subject: Re: [PATCH] fs: Return EOPNOTSUPP if block layer does not support REQ_NOWAIT
Date: Tue, 18 Dec 2018 05:53:54 -0600	[thread overview]
Message-ID: <20181218115354.x45jvpftvwcu2aqj@merlin> (raw)
In-Reply-To: <20181216213504.GB10644@dastard>

On  8:35 17/12, Dave Chinner wrote:
> > 
> > I was not too happy getting it all the way down to block layer either.
> > The multi-devices makes it worse. However, here we are and we need to
> > tell the user that RWF_NOWAIT is not supported in this environment.
> RWF_NOWAIT matters for filesystems much more than the underlying
> block device. If the application is accessing the blockd evice
> directly, then yes, RWF_NOWAIT support in the block device matters.
> But when the IO is being done through the filesystem it's far more
> important to avoid blocking on filesystem locks that whatever the
> block device does....
> Hence I think that if the bio is coming from a filesystem,
> REQ_NOWAIT should always be accepted or bounced with EAGAIN and
> never failed with EOPNOTSUPP. It just makes no sense at all for
> filesytsem based IO....

It was initially suggested where the block layer would retry getting
a bio in get_request(). While request based devices were fine, the bio
based ones such as MD needed extra work. However, when I actually got
down to writing code for multi-device, it got more hurdles than
solutions primarily in the area of bio merging.

RWF_NOWAIT should have been restricted to filesystems and I think we
should do away (or at least ignore) REQ_NOWAIT for now.


  reply	other threads:[~2018-12-18 11:53 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-13 11:53 Goldwyn Rodrigues
2018-12-13 12:04 ` Avi Kivity
2018-12-13 14:24   ` Christoph Hellwig
2018-12-13 15:44     ` Goldwyn Rodrigues
2018-12-16 10:45     ` Avi Kivity
2018-12-17 17:38       ` Christoph Hellwig
2018-12-18 11:55         ` Goldwyn Rodrigues
2018-12-20 15:32           ` Avi Kivity
2018-12-13 16:27 ` Matthew Wilcox
2018-12-13 19:04   ` Goldwyn Rodrigues
2018-12-13 22:43 ` Dave Chinner
2018-12-14 17:09   ` Goldwyn Rodrigues
2018-12-16 21:35     ` Dave Chinner
2018-12-18 11:53       ` Goldwyn Rodrigues [this message]
2020-07-22 16:08 ` Avi Kivity
2020-07-28 13:38   ` Goldwyn Rodrigues
2020-07-28 13:47     ` Avi Kivity
2020-07-31 13:11   ` Christoph Hellwig

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