From: Ric Wheeler <ricwheeler@gmail.com>
To: Dave Chinner <david@fromorbit.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: Sun, 17 Feb 2019 18:42:59 -0500 [thread overview]
Message-ID: <46540876-c222-0889-ddce-44815dcaad04@gmail.com> (raw)
In-Reply-To: <20190217210948.GB14116@dastard>
On 2/17/19 4:09 PM, Dave Chinner wrote:
> 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.
I think the variability makes life really miserable for layers above it.
Might be worth constructing some tooling that we can use to validate or shame
vendors over - testing things like a full device discard, discard of fs block
size and big chunks, discard against already discarded, etc.
Regards,
Ric
next prev parent reply other threads:[~2019-02-17 23:43 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
2019-02-17 23:42 ` Ric Wheeler [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=46540876-c222-0889-ddce-44815dcaad04@gmail.com \
--to=ricwheeler@gmail.com \
--cc=david@fromorbit.com \
--cc=linux-block@vger.kernel.org \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-xfs@vger.kernel.org \
--cc=lsf-pc@lists.linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).