Messages in this thread | | | Subject | Re: [PATCH 2/2] loop: Better discard support for block devices | From | "Martin K. Petersen" <> | Date | Wed, 05 Dec 2018 22:15:10 -0500 |
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Evan,
> Ah, I see. But I think it's useful to reflect max_discard_sectors, > max_write_zeroes_sectors, discard_granularity, and discard_alignment > from the block device to the loop device. With the exception of > discard_alignment, these parameters are visible via sysfs,
discard_alignment is visible in sysfs, just not in the queue directory since alignment can be different on a per-partition basis. So there is one discard_alignment at the root of each /sys/block/foo directory and one for each partition subdirectory. This mirrors the alignment_offset variable which indicates a partitions alignment wrt. the underlying physical block size.
That said, there are not many devices that actually report a non-zero discard alignment so it's not as useful as the device manufacturers (that were looking for an implementation shortcut) envisioned.
> I'm not totally sure about discard_alignment, that seems to be useful > in cases of merging blk requests. So I can stop mirroring that one if > it's harmful or not helpful. But unless it's a nak, I'd really love to > keep most of the mirroring. In which case the bool doesn't do a whole > lot of simplifying.
I think it's fine to export these. The block device topology was explicitly designed to be stackable like this.
-- Martin K. Petersen Oracle Linux Engineering
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