>>>>> "Tom" == Tom Yan <tom.t...@gmail.com> writes:
Tom> Well that is actually the minimum. Modern SSDs often support more Tom> than one-block payload (e.g. 8, 16...). It's just our SCSI disk Tom> driver statically limit it to the minimum. Though it allows only Tom> 0xffffffff / 512 = 8388607 (SD_MAX_WS16_BLOCKS) blocks per WRITE Tom> SAME (16) command anyway, Yes, because that's the biggest command we can express in the block layer. Tom> so we can at most allow only a 2-block (well, or 3-block) payload. We tried turning on multi block payloads and it was a massive disaster. Many drives reported that they supported 8 block payloads but actually didn't. Instead of playing the blacklist game we capped it at a single sector. Many drives from different vendors were affected by this. So we'd have to make multi block payloads an explicit opt-in like we did for discard_zeroes_data. However, given that "big" discards are mainly done synchronously when creating filesystems, I am not sure there is any real benefit to this. -- Martin K. Petersen Oracle Linux Engineering
