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

[Ming Lei]

On Mon, Jun 19, 2017 at 11:18 PM, Christoph Hellwig <hch at lst.de> wrote:
> 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.

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

Thanks,
Ming Lei