[PATCH v9 3/8] block: add check when merging zone device pages

[Christoph Hellwig]

On Thu, Aug 25, 2022 at 09:24:20AM -0600, Logan Gunthorpe wrote:
> Consecutive zone device pages should not be merged into the same sgl
> or bvec segment with other types of pages or if they belong to different
> pgmaps. Otherwise getting the pgmap of a given segment is not possible
> without scanning the entire segment. This helper returns true either if
> both pages are not zone device pages or both pages are zone device
> pages with the same pgmap.
> 
> Add a helper to determine if zone device pages are mergeable and use
> this helper in page_is_mergeable().
> 
> Signed-off-by: Logan Gunthorpe <logang at deltatee.com>

Looks good:

Reviewed-by: Christoph Hellwig <hch at lst.de>