Re: [PATCH 7/8] block: refactor the bounce buffering code

[Christoph Hellwig <hch@lst.de>]

On Thu, Mar 18, 2021 at 11:29:50AM +0000, Matthew Wilcox wrote:
> On Thu, Mar 18, 2021 at 07:39:22AM +0100, Christoph Hellwig wrote:
> > @@ -536,7 +518,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
> >  					b->max_write_zeroes_sectors);
> >  	t->max_zone_append_sectors = min(t->max_zone_append_sectors,
> >  					b->max_zone_append_sectors);
> > -	t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);
> > +	t->bounce = min_not_zero(t->bounce, b->bounce);
> 
> I see how min_not_zero() made sense when it was a pfn.  Does it still
> make sense now it's an enum?  I would have thought it'd now be 'max()',
> given the definitions later on.

Actually, blk_stack_limits should not look at ->bounce_pfn / ->bounce
at all.  blk_queue_bounce is only called my blk_mq_submit_bio, and
the only stacked blk-mq driver (dm-mpath) does not need bouncing.

I'll add a patch to fix this up to the front of the series.