Messages in this thread | | | Subject | Re: next bio iters break discard? | From | "Martin K. Petersen" <> | Date | Mon, 13 Jan 2014 23:06:33 -0500 |
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>>>>> "Kent" == Kent Overstreet <kmo@daterainc.com> writes:
Kent,
Kent> I think for discards we can deal with this easily enough - Kent> __blk_recalc_rq_segments() will have to special case them - but Kent> there's a similar (but worse) issue with WRITE_SAME, and looking Kent> at the code it does attempt to merge WRITE_SAME requests too.
DISCARD bios have no payload going down the stack. They get a payload attached in the sd driver and will therefore have a single bvec at completion time.
WRITE_SAME bios have a single bvec payload throughout their lifetime.
For both these types of requests we never attempt to merge the actual payloads. But the block range worked on may shrink or grow as the bio is split or merged going down the stack.
IOW, DISCARD, WRITE SAME and the impending COPY requests do not have a 1:1 mapping between the block range worked on and the size of any bvecs attached. Your recent changes must have changed the way we handled that in the past.
I'll take a look tomorrow...
-- Martin K. Petersen Oracle Linux Engineering
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