Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [PATCH 3/3] blkdev: honor discard_granularity in blkdev_issue_discard() | Date | Mon, 02 May 2011 12:10:41 -0400 |
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"Martin K. Petersen" <martin.petersen@oracle.com> writes:
>>>>>> "Lukas" == Lukas Czerner <lczerner@redhat.com> 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.
Cheers, Jeff
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