On Mon, Aug 22, 2016 at 8:25 PM, Damien Le Moal <damien.lem...@hgst.com> wrote: > > Shaun, > > On 8/23/16 09:22, Shaun Tancheff wrote: >> On Mon, Aug 22, 2016 at 6:57 PM, Damien Le Moal <damien.lem...@hgst.com> >> wrote:
>> Also you may note that in my patch to get Host Aware working >> with the zone cache I do not include the runt zone in the cache. > > Why not ? The RB-tree will handle it just fine (the insert and lookup > code as Hannes had them was not relying on a constant zone size). A good point. I didn't pay too much attention while brining this forward. I think a few of my hacks may be pointless now. I'll try to rework it and get rid of the runt check. >> So as it sits I need this fallback otherwise doing blkdiscard over >> the whole device ends in a error, as well as mkfs.f2fs et. al. > > Got it, but I do not see a problem with including it. I have not checked > the code, but the split of a big discard call into "chunks" should be > already handling the last chunk and make sure that the operation does > not exceed the device capacity (in any case, that's easy to fix in the > sd_zbc_setup_discard code). Yes I agree the split of big discards does handle the last chunk correctly. >>> Some 10TB host managed disks out there have 1% conventional zone space, >>> that is 100GB of capacity. When issuing a "reset all", doing a write >>> same in these zones will take forever... If the user really wants zeroes >>> in those zones, let it issue a zeroout. >>> >>> I think that it would a better choice to simply not report >>> discard_zeroes_data as true and do nothing for conventional zones reset. >> >> I think that would be unfortunate for Host Managed but I think it's >> the right choice for Host Aware at this time. So either we base >> it on disk type or we have some other config flag added to sysfs. > > I do not see any difference between host managed and host aware. Both > define the same behavior for reset, and both end up in a NOP for > conventional zone reset (no data "erasure" required by the standard). > For write pointer zones, reading unwritten LBAs returns the > initialization pattern, with the exception of host-managed disks with > the URSWRZ bit set to 0. But that case is covered in sd.c, so the > behavior is consistent across all models. So why forcing data zeroing > when the standards do not mandate it ? Well you do have point. It appears to be only mkfs and similar tools that are really utilizing discard zeros data at the moment. I did a quick test: mkfs -t ext4 -b 4096 -g 32768 -G 32 \ -E lazy_itable_init=0,lazy_journal_init=0,offset=0,num_backup_sb=0,packed_meta_blocks=1,discard \ -O flex_bg,extent,sparse_super2 - discard zeroes data true - 3 minutess - discard zeroes data false - 6 minutes So for the smaller conventional space on the current HA drive there is some advantage to enabling discard zeroes data. However for a larger conventional space you are correct the overall impact is worse performance. For some reason I had been assuming that some file systems used or relied on discard zeroes data during normal operation. Now that I am looking for that I don't seem to be finding any evidence of it, so aside from mkfs I don't have as good an argument discard zeroes data as I though I did. Regards, Shaun
