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SubjectRe: [PATCH 3/3] blkdev: honor discard_granularity in blkdev_issue_discard()
"Martin K. Petersen" <> writes:

>>>>>> "Lukas" == Lukas Czerner <> writes:
> Lukas> As Jeff Moyer pointed out we do not honor discard granularity
> Lukas> while submitting REQ_DISCARD bios of size smaller than
> Lukas> max_discard_sectors. That fact might have unwanted consequences
> Lukas> of device ignoring the request, or even worse if device firmware
> Lukas> is buggy.
> We've discussed this before and the consensus was not to do it. The
> granularity is a hint, not a hard limit like max_discard_sectors.
> We want the reporting to be comprehensive throughout the block layer. If
> we start aligning to the granularity at the top we lose information for
> stacked devices below with a finer granularity.
> So if we were to align to the granularity we'd want to do it at the
> bottom of the stack when we issue the command to the device. We've had a
> few proposed patches to did that but so far we've only found one device
> where it made a difference. And that case didn't justify adding a quirk.

Hm, I wonder where it makes sense to document this. Maybe
Documentation/block/queue-sysfs.txt, but I admit I wouldn't have looked
there while reviewing this code.


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