Re: Discard support (was Re: [PATCH] swap: send callback when swap slot is freed)

James Bottomley wrote:

For SSDs, the FTL has to have a separate operation: erase.  Now, one
could see the correct implementation simply moving the sectors from the
in-use list to the to be cleaned list and still do the cleaning in the
background: that would be constant cost (but, again, likely expensive).
Of course, if SSD vendors decided to erase on the spot when seeing TRIM,
this wouldn't be true ...

..

The SSDs based upon the Indilinx Barefoot controller appear to do
the erase on the spot, along with a fair amount of garbage collection.
The overhead does vary by size of the TRIM operation (number of sectors
and extents), but even a single-sector TRIM has very high overhead.

Samsung also now has SSDs at retail with TRIM.
I don't have one of those here.