From: Sergei Trofimovich <slyich@gmail.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Josef Bacik <josef@toxicpanda.com>,
Christopher Price <pricechrispy@gmail.com>,
anand.jain@oracle.com, boris@bur.io, clm@fb.com,
dsterba@suse.com, linux-btrfs@vger.kernel.org,
regressions@leemhuis.info, regressions@lists.linux.dev
Subject: Re: [6.2 regression][bisected]discard storm on idle since v6.1-rc8-59-g63a7cb130718 discard=async
Date: Thu, 23 Mar 2023 22:26:06 +0000 [thread overview]
Message-ID: <20230323222606.20d10de2@nz> (raw)
In-Reply-To: <ZBq+ktWm2gZR/sgq@infradead.org>
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On Wed, 22 Mar 2023 01:38:42 -0700
Christoph Hellwig <hch@infradead.org> wrote:
> On Tue, Mar 21, 2023 at 05:26:49PM -0400, Josef Bacik wrote:
> > We got the defaults based on our testing with our workloads inside of
> > FB. Clearly this isn't representative of a normal desktop usage, but
> > we've also got a lot of workloads so figured if it made the whole
> > fleet happy it would probably be fine everywhere.
> >
> > That being said this is tunable for a reason, your workload seems to
> > generate a lot of free'd extents and discards. We can probably mess
> > with the async stuff to maybe pause discarding if there's no other
> > activity happening on the device at the moment, but tuning it to let
> > more discards through at a time is also completely valid. Thanks,
>
> FYI, discard performance differs a lot between different SSDs.
> It used to be pretty horrible for most devices early on, and then a
> certain hyperscaler started requiring decent performance for enterprise
> drives, so many of them are good now. A lot less so for the typical
> consumer drive, especially at the lower end of the spectrum.
>
> And that jut NVMe, the still shipping SATA SSDs are another different
> story. Not helped by the fact that we don't even support ranged
> discards for them in Linux.
Josef, what did you use as a signal to detect what value was good
enough? Did you crank up the number until discard backlog clears up in a
reasonable time?
I still don't understand what I should take into account to change the
default and whether I should change it at all. Is it fine if the discard
backlog takes a week to get through it? (Or a day? An hour? A minute?)
Is it fine to send discards as fast as device allows instead of doing 10
IOPS? Does IOPS limit consider a device wearing tradeoff? Then low IOPS
makes sense. Or IOPS limit is just a way to reserve most bandwidth to
non-discard workloads? Then I would say unlimited IOPS as a default
would make more sense for btrfs.
--
Sergei
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next prev parent reply other threads:[~2023-03-23 22:26 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-20 22:40 [6.2 regression][bisected]discard storm on idle since v6.1-rc8-59-g63a7cb130718 discard=async Christopher Price
2023-03-21 21:26 ` Josef Bacik
2023-03-22 8:38 ` Christoph Hellwig
2023-03-23 22:26 ` Sergei Trofimovich [this message]
2023-04-04 10:49 ` Linux regression tracking (Thorsten Leemhuis)
2023-04-04 16:04 ` Christoph Hellwig
2023-04-04 16:20 ` Roman Mamedov
2023-04-04 16:27 ` Christoph Hellwig
2023-04-04 23:37 ` Damien Le Moal
2023-04-04 18:15 ` Chris Mason
2023-04-04 18:51 ` Boris Burkov
2023-04-04 19:22 ` David Sterba
2023-04-04 19:39 ` Boris Burkov
2023-04-05 8:17 ` Linux regression tracking (Thorsten Leemhuis)
2023-04-10 2:03 ` Michael Bromilow
2023-04-11 17:52 ` David Sterba
2023-04-11 18:15 ` Linux regression tracking (Thorsten Leemhuis)
2023-04-04 19:08 ` Sergei Trofimovich
2023-04-05 6:18 ` Christoph Hellwig
2023-04-05 12:01 ` Chris Mason
2023-04-04 18:23 ` Boris Burkov
2023-04-04 19:12 ` Sergei Trofimovich
[not found] <Y/+n1wS/4XAH7X1p@nz>
2023-03-02 8:04 ` Linux regression tracking #adding (Thorsten Leemhuis)
2023-04-04 10:52 ` Linux regression tracking #update (Thorsten Leemhuis)
2023-04-21 13:56 ` Linux regression tracking #update (Thorsten Leemhuis)
[not found] ` <94cf49d0-fa2d-cc2c-240e-222706d69eb3@oracle.com>
[not found] ` <20230302105406.2cd367f7@nz>
2023-03-15 11:44 ` Linux regression tracking (Thorsten Leemhuis)
2023-03-15 16:34 ` Sergei Trofimovich
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