Re: TRIM vs UNMAP vs WRITE SAME and thin devices

["David Woodhouse" <dwmw2@infradead.org>]

> On Sat, Feb 07, 2009 at 09:53:06AM -0500, Ric Wheeler wrote:
>> I have been poked at by some vendors about the status of our support for
>> the virtually/thinly provisioned luns since they are getting close to
>> being able to test with real devices.
>>
>> My quick summary is that we most of the work so far has been done
>> without any real hardware to play with - in 2.6.29-rc3, I don't see any
>> low level ATA or SCSI bits that turn requests tagged with REQ_DISCARD
>> into the specific ATA or SCSI commands. Did I miss something & if not,
>> do we have plans to push anything upstream soonish?
>
> Bearing in mind that I'm now three weeks behind on email, you might want
> to look at
> http://git.kernel.org/?p=linux/kernel/git/willy/ssd.git;a=shortlog;h=trim-20081231
> which has at least one known bug (fixed by Dave Woodhouse and Ben
> Herrenschmidt).  I'll be able to give a more coherent answer in a few
> days.  Or maybe Dave will beat me to it ;-)

Ben's suggestion was that the IDE core wouldn't be sending the payload of
the command because it looks at the R/W bit... which is clear (read) in
our discard requests ATM. Making them appear to be writes is simple enough
though. I gave an updated test kernel to the Sandisk folks but haven't got
results back from them yet.