Re: [PATCH v11 5/9] lib/scatterlist: add check when merging zone device pages

[Chaitanya Kulkarni <chaitanyak@nvidia.com>]

On 10/21/22 10:41, 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.
> 
> Factor out the check for page mergability into a pages_are_mergable()
> helper and add a check with zone_device_pages_are_mergeable().
> 
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
>   lib/scatterlist.c | 25 +++++++++++++++----------
>   1 file changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> index c8c3d675845c..a0ad2a7959b5 100644
> --- a/lib/scatterlist.c
> +++ b/lib/scatterlist.c
> @@ -410,6 +410,15 @@ static struct scatterlist *get_next_sg(struct sg_append_table *table,
>   	return new_sg;
>   }
>   
> +static bool pages_are_mergeable(struct page *a, struct page *b)
> +{
> +	if (page_to_pfn(a) != page_to_pfn(b) + 1)
> +		return false;
> +	if (!zone_device_pages_have_same_pgmap(a, b))
> +		return false;
> +	return true;
> +}
> +


not sure if it makes sense to make it inline ? either way,

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

-ck