Re: [PATCH] libata: Whitelist SSDs that are known to properly return zeroes after TRIM

[Tejun Heo <tj@kernel.org>]

Hello,

On Thu, Dec 04, 2014 at 09:13:22PM -0500, Martin K. Petersen wrote:
> Tejun> If there's something on the horizon which would solve the
> Tejun> identification problem and we only have to worry about the
> Tejun> current batch of devices, whitelisting can be useful but
> Tejun> otherwise I'm not sure this is a good idea.
> 
> There isn't :( The only saving grace is that SSDs are gravitating
> towards NVMe and other non-ATA interfaces.

Yeap, that's true.  This whole thing is on the way out.

> I've already tightened up things in SCSI so we now prefer WRITE SAME
> which does give hard guarantees unlike UNMAP. But because we use WRITE
> SAME in the libata SATL it is imperative that we change our internal
> flagging to be equally restrictive.

Can you please elaborate this in the changelog and add comments
explaning why ATA_HORKAGE_ZERO_AFTER_TRIM is necessary and how it's
used?

> I just feel bad about disabling the feature for the many existing users
> (and there are quite a few) that are using well-behaved drives in their
> RAID deployments. And the filesystem folks have been begging for the
> zeroout discard variant that I posted a few weeks ago. So the users are
> there. I'm just trying to accommodate them the best I can given the lame
> spec.

Can you please explain further the practical gains of using trims
which guarantee zeroing?

Thanks.

-- 
tejun