Re: Using async discard by default with SSDs?

[Neal Gompa <ngompa13@gmail.com>]

On Wed, Jul 27, 2022 at 8:01 AM David Sterba <dsterba@suse.cz> wrote:
>
> On Wed, Jul 27, 2022 at 10:50:01AM -0400, Chris Murphy wrote:
> > On Tue, Jul 26, 2022, at 6:10 PM, Chris Murphy wrote:
> > > On Tue, Jul 26, 2022, at 5:36 PM, David Sterba wrote:
> > >> What is quickly here?
> > >
> > > Seconds, less than a minute, all the blocks pointed to by backup roots
> > > are empty (zeros).
> > >
> > >  The default timeout is set to 2 minutes and that's
> > >> what I've seen when testing that on a fresh filesystem.
> > >
> > > Ok I'll retest with 5.19 series. The last time I tested time to drive
> > > gc backup rootswas circa 5.8.
> >
> > With 5.19, backup roots remain available for a surprisingly long time,
> > definitely more than 2 minutes. It's not an exhaustive test, just a
> > dozen samples over a half hour, but I never once saw zeros returned.
> > Two out of those dozen, I saw the block already overwritten with a
> > leaf of a newer generation and a completely different owner (e.g. csum
> > tree written at the block address for the backup tree root)  - which
> > would make that backup root useless.
> >
> > 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.

It would definitely be nice to see this for 5.20. :)


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