Re: [PATCH V1 9/9] iommufd: optimize file mapping

[Jason Gunthorpe <jgg@nvidia.com>]

On Sat, Sep 14, 2024 at 06:05:58AM -0700, Steve Sistare wrote:
> Avoid expanding a huge folio into multiple upages[] in pin_memfd_pages by
> adding a page count nupages[i] for each upages[i].  Provide the function
> batch_from_pages_num to efficiently add counted pages to a pfn_batch.


> @@ -695,6 +717,7 @@ static unsigned long batch_rw(struct pfn_batch *batch, void *data,
>  struct pfn_reader_user {
>  	struct page **upages;
>  	unsigned long upages_num;
> +	u32 *nupages;

I think you'd be better to have

union {
   struct page **upages;
   struct folio **ufolio;
};

Add some batch_from_folios() to do the logic

The flow would want to work the same as the pages where you fill in
the ufolios array and then trickle it out into the batch

Jason