Re: [dm-devel] [PATCH v5 01/11] block: make generic_make_request handle arbitrarily sized bios

From: Martin K. Petersen
Date: Sat Aug 08 2015 - 12:21:13 EST

>>>>> "Mike" == Mike Snitzer <snitzer@xxxxxxxxxx> writes:

Mike> This will translate to all intermediate layers that might split
Mike> discards needing to worry about granularity/alignment too
Mike> (e.g. how dm-thinp will have to care because it must generate
Mike> discard mappings with associated bios based on how blocks were
Mike> mapped to thinp).

The fundamental issue here is that alignment and granularity should
never, ever have been enforced at the top of the stack. Horrendous idea
from the very beginning.

For the < handful of braindead devices that get confused when you do
partial or misaligned blocks we should have had a quirk that did any
range adjusting at the bottom in sd_setup_discard_cmnd().

There's a reason I turned discard_zeroes_data off for UNMAP!

Wrt. the range size I don't have a problem with capping at the 32-bit
bi_size limit. We probably don't want to send commands much bigger than
that anyway.

Martin K. Petersen Oracle Linux Engineering
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