On Thu, 2019-01-10 at 16:55 +0100, Zdenek Kabelac wrote: > Dne 10. 01. 19 v 16:23 Martin Wilck napsal(a): > > 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. > > I assume this is valid request for enhancement of thin-pool target. > However this 'WRITE_SAME' or whatever scsi low-level command is > that is > basically targeted for thinLV user. > > So in this case the most effective 'zeroing' of thinLV areas is its > discard. That's what I have in mind. Basically, one could implement a "write_zeroes" operation in a similar manner as discard is implemented now. We'd just need to be careful with the case where a write_zeroes request isn't aligned to chunk size (aka discard_granularity), and instead of a noop, either return an error, or fall back to "slow" zeroing for the unaligned pieces. I believe that wouldn't be a big problem in practice - prudent users would respect the granularity anyway. Regards Martin -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
