[dm-devel] [PATCH 01/10] pktcdvd: remove the call to blk_queue_bounce

[Christoph Hellwig]

On Mon, Jun 19, 2017 at 11:13:46PM +0800, Ming Lei wrote:
> On Mon, Jun 19, 2017 at 11:00 PM, Christoph Hellwig <hch at lst.de> wrote:
> > On Mon, Jun 19, 2017 at 10:34:36PM +0800, Ming Lei wrote:
> >> blk_queue_make_request() sets bounce for any highmem page for long time,
> >> and in theory this patch might cause regression on 32bit arch, when
> >> the controller can't handle higmem page really(especially in case of PAE), so
> >> we may need to be careful about this change, especially on some old hardware.
> >
> > Which controller?
> 
> I don't know.
> 
> IMO, we can't just remove it because it is a bio based driver, the
> bounce is not related with
> a bio or req based driver, and it depends if the controller can handle
> highmem page.

pktcdvd is a stacking driver and forwards all data through either
generic_make_request or blk_rq_map_kern + blk_execute_rq,
both of which call blk_queue_bounce internally.