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SubjectRe: 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.

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