From: Dave Chinner <david@fromorbit.com>
To: Ric Wheeler <ricwheeler@gmail.com>
Cc: lsf-pc@lists.linux-foundation.org,
linux-xfs <linux-xfs@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-ext4 <linux-ext4@vger.kernel.org>,
linux-btrfs <linux-btrfs@vger.kernel.org>,
linux-block@vger.kernel.org
Subject: Re: [LSF/MM TOPIC] More async operations for file systems - async discard?
Date: Mon, 18 Feb 2019 08:09:48 +1100 [thread overview]
Message-ID: <20190217210948.GB14116@dastard> (raw)
In-Reply-To: <92ab41f7-35bc-0f56-056f-ed88526b8ea4@gmail.com>
On Sun, Feb 17, 2019 at 03:36:10PM -0500, Ric Wheeler wrote:
> One proposal for btrfs was that we should look at getting discard
> out of the synchronous path in order to minimize the slowdown
> associated with enabling discard at mount time. Seems like an
> obvious win for "hint" like operations like discard.
We already have support for that. blkdev_issue_discard() is
synchornous, yes, but __blkdev_issue_discard() will only build the
discard bio chain - it is up to the caller to submit and wait for it.
Some callers (XFS, dm-thinp, nvmet, etc) use a bio completion to
handle the discard IO completion, hence allowing async dispatch and
processing of the discard chain without blocking the caller. Others
(like ext4) simply call submit_bio_wait() to do wait synchronously
on completion of the discard bio chain.
> I do wonder where we stand now with the cost of the various discard
> commands - how painful is it for modern SSD's?
AIUI, it still depends on the SSD implementation, unfortunately.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2019-02-17 21:09 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-17 20:36 [LSF/MM TOPIC] More async operations for file systems - async discard? Ric Wheeler
2019-02-17 21:09 ` Dave Chinner [this message]
2019-02-17 23:42 ` Ric Wheeler
2019-02-18 2:22 ` Dave Chinner
2019-02-18 22:30 ` Ric Wheeler
2019-02-20 23:47 ` Keith Busch
2019-02-21 20:08 ` Dave Chinner
2019-02-21 23:55 ` Jeff Mahoney
2019-02-22 3:01 ` Martin K. Petersen
2019-02-22 6:15 ` Roman Mamedov
2019-02-22 14:12 ` Martin K. Petersen
2019-02-22 2:51 ` Martin K. Petersen
2019-02-22 16:45 ` Keith Busch
2019-02-27 11:40 ` Ric Wheeler
2019-02-27 13:24 ` Matthew Wilcox
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