[dm-devel] dm thin pool discarding

[Martin Wilck]

On Thu, 2019-01-10 at 16:08 +0100, Zdenek Kabelac wrote:
> Dne 10. 01. 19 v 14:41 Martin Wilck napsal(a):
> > 
> > I for one would find it very attractive if dm-thin had a mode
> > supporting fast zeroout.
> 
> I believe '/sys/block/*/queue/discard_zeroes_data  is now always
> returning 
> false for any device as it's been considered as unreliable logic.
> 
> So using 'discard' for zeroing is not really an option here.

True. But we have "write_zeroes_max_bytes" instead. In device mapper
terms, it's "num_write_zeroes_bios", which isn't set for dm-thin. With
the logic outlined above, it could be set, AFAICT.

Thanks,
Martin