Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation

[Jamie Lokier]

Jeff Moyer wrote:
> James Bottomley <James.Bottomley@xxxxxxx> writes:
> 
> > Not stepping into the debate: I'm happy to see punch go to the mapping
> > data and FITRIM pick it up later.
> >
> > However, I think it's time to question whether we actually still want to
> > allow online discard at all.  Most of the benchmarks show it to be a net
> 
> Define online discard, please.
> 
> > lose to almost everything (either SSD or Thinly Provisioned arrays), so
> > it's become an "enable this to degrade performance" option with no
> > upside.
> 
> Some SSDs very much require TRIMming to perform well as they age.  If
> you're suggesting that we move from doing discards in journal commits to
> a batched discard, like the one Lukas implemented, then I think that's
> fine.  If we need to reintroduce the finer-grained discards due to some
> hardware changes in the future, we can always do that.

"Growable" virtual disks benefit from it too, if it frees up a lot of space.

Windows has some ability to trim unused space in NTFS on virtual disks
for this reason; I'm not sure if it's an online or offline procedure.

Online trim may be slow, but offline would be awfully inconvenient
when an fs is big and needed for a live system, or when it's your root fs.

-- Jamie
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