Lukas, > Do we also know that the blocks were discarded as we do with > BLKDISCARD ? There never was a way to know for sure. ATA DSM TRIM and SCSI UNMAP are hints by definition. We attempted to bend their semantics towards getting predictable behavior but ultimately failed. Too many corner cases. > As I mentioned before. We relied on discard_zeroes_data in mkfs.ext4 > to make sure that inode tables are zeroed after discard. The point is that you shouldn't have an if (discard_zeroes_data) conditional in the first place. - If you need to dellocate a block range and you don't care about its contents in the future, use BLKDISCARD / FL_PUNCH_HOLE. - If you need to zero a block range, use BLKZEROOUT / FL_ZERO_RANGE. So the mkfs usage model should essentially be: - DISCARD the entire partition/device block range - ZEROOUT the inode tables and other areas where you need zeroes on future reads And that should be the approach regardless of whether your device is a disk drive, an SSD, an NVMe device a SCSI array or whatever. DISCARD old contents, ZEROOUT the pieces you care about. No conditionals or trying to do things differently based on device capabilities. -- Martin K. Petersen Oracle Linux Engineering
