Re: Using async discard by default with SSDs?

[David Sterba <dsterba@suse.cz>]

On Wed, Jul 27, 2022 at 11:14:01AM -0400, Chris Murphy wrote:
> 
> 
> On Wed, Jul 27, 2022, at 10:56 AM, David Sterba wrote:
> > On Wed, Jul 27, 2022 at 10:50:01AM -0400, Chris Murphy wrote:
> >> What is a likely target kernel version to make discard=async the
> >> default? The merge window for 5.20 closes August 14. Is 5.21 a
> >> practical target?
> >
> > The changes for the next merge window are supposed to be done a week or
> > two before it opens, but as this is a simple change I think I can
> > squeeze it in.
> 
> For 5.20?

Yes, 5.20.

> I'm not aware of any conflict with fstrim. But I wonder if there's a
> preference to coordinate the change with util-linux folks? 

The -o discard and fstrim are independent and can be used at the same
time.

> Currently, util-linux provides fstrim.timer which runs fstrim.service every Monday at 00:00 local time. The command is:
> 
> ExecStart=/usr/sbin/fstrim --listed-in /etc/fstab:/proc/self/mountinfo --verbose --quiet-unsupported
> 
> I'm not sure how they'd go about implementing an exception for Btrfs,
> either entirely or only if a discard mount option is detected. But I
> can ask?

No need for an exception, during mount btrfs track ranges that have been
trimmed and skips them when discard is requested by fstrim, so it's a
no-op.