Hi, On 2021-01-04 14:17:05 -0500, Theodore Ts'o wrote: > One thing to note is that there are some devices which support a write > zeros operation, but where it is *less* performant than actually > writing zeros via DMA'ing zero pages. Yes, that's insane. > Unfortunately, there are a insane devices out there.... That doesn't surprise me at all, unfortunately. I'm planning to send a proposal to allow disabling a device's use of fua for similar reasons... > That doesn't meant that your proposal shouldn't be adopted. But it > would be a good idea to have some kind of way to either allow some > kind of tuning knob to disable the user of zeroout (either in the > block device, file system, or in userspace), and/or some kind of way > to try to automatically figure out whether using zeroout is actually a > win, since most users aren't going to be up to adjusting a manual > tuning knob. A block device know seems to make sense to me. There already is /sys/block/*/queue/write_zeroes_max_bytes it seems like it could make sense to add a sibling entry to allow tuning that? Presumably with a quirks (as suggested by Matthew) to choose a sensible default? It's not quite analogous, but there's for max_hw_sectors_kb/max_sectors_kb and discard_max_bytes / discard_max_hw_bytes, and it seems like something vaguely in that direction could make sense? Greetings, Andres Freund
