On Mon, Jun 19, 2017 at 11:18 PM, Christoph Hellwig [off-list ref] wrote:

On Mon, Jun 19, 2017 at 11:13:46PM +0800, Ming Lei wrote:

quoted

On Mon, Jun 19, 2017 at 11:00 PM, Christoph Hellwig [off-list ref] wrote:

quoted

On Mon, Jun 19, 2017 at 10:34:36PM +0800, Ming Lei wrote:

quoted

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.

OK, thanks for explaining, then looks it isn't needed from the start.

Thanks,
Ming Lei