On Tue, May 03, 2022 at 11:12:04AM +0200, Pankaj Raghav wrote: > Hi Johannes, > On 2022-05-03 00:07, Johannes Thumshirn wrote: > >> There was an effort previously [1] to add support to non po2 devices via > >> device level emulation but that was rejected with a final conclusion > >> to add support for non po2 zoned device in the complete stack[2]. > > > > Hey Pankaj, > > > > One thing I'm concerned with this patches is, once we have npo2 zones (or to be precise > > not fs_info->sectorsize aligned zones) we have to check on every allocation if we still > > have at least have fs_info->sectorsize bytes left in a zone. If not we need to > > explicitly finish the zone, otherwise we'll run out of max active zones. > > > This commit: `btrfs: zoned: relax the alignment constraint for zoned > devices` makes sure the zone size is BTRFS_STRIPE_LEN aligned (64K). So > even the npo2 zoned device should be aligned to `fs_info->sectorsize`, > which is typically 4k. > > This was one of the comment that came from David Sterba: > https://lore.kernel.org/all/20220315142740.GU12643@xxxxxxxxxxxxx/ > where he suggested to have some sane alignment for the zone sizes. My idea of 'sane' value would be 1M, that we have 4K for sectors is because of the 1:1 mapping to pages, but RAM sizes are on a different scale than storage devices. The 4K is absolute minimum but if the page size is taken as a basic constraint, ARM has 64K and there are some 256K arches.
