On 10/18/18 7:18 AM, Ming Lei wrote:

Now we only check if DMA IO buffer is aligned to queue_dma_alignment()
for pass-through request, and it isn't done for normal IO request.

Given the check has to be done on each bvec, it isn't efficient to add the
check in generic_make_request_checks().

This patch addes one WARN in blk_queue_split() for capturing this issue.

I don't want to do this, because then we are forever doomed to
have something that fully loops a bio at submission time. I
absolutely hate the splitting we have and the need for it,
hopefully it can go away for a subset of IOs at some point.

In many ways, this seems to be somewhat of a made-up problem, I don't
recall a single bug report for something like this over decades of
working with the IO stack. 512b alignment restrictions for DMA seems
absolutely insane. I know people claim they exist, but clearly that
isn't a hard requirement or we would have been boned years ago.

-- 
Jens Axboe