Re: [PATCH v5 8/8] device-dax: compound devmap support

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, Nov 12, 2021 at 04:08:24PM +0100, Joao Martins wrote:

> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index a65c67ab5ee0..0c2ac97d397d 100644
> +++ b/drivers/dax/device.c
> @@ -192,6 +192,42 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
>  }
>  #endif /* !CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
>  
> +static void set_page_mapping(struct vm_fault *vmf, pfn_t pfn,
> +			     unsigned long fault_size,
> +			     struct address_space *f_mapping)
> +{
> +	unsigned long i;
> +	pgoff_t pgoff;
> +
> +	pgoff = linear_page_index(vmf->vma, ALIGN(vmf->address, fault_size));
> +
> +	for (i = 0; i < fault_size / PAGE_SIZE; i++) {
> +		struct page *page;
> +
> +		page = pfn_to_page(pfn_t_to_pfn(pfn) + i);
> +		if (page->mapping)
> +			continue;
> +		page->mapping = f_mapping;
> +		page->index = pgoff + i;
> +	}
> +}
> +
> +static void set_compound_mapping(struct vm_fault *vmf, pfn_t pfn,
> +				 unsigned long fault_size,
> +				 struct address_space *f_mapping)
> +{
> +	struct page *head;
> +
> +	head = pfn_to_page(pfn_t_to_pfn(pfn));
> +	head = compound_head(head);
> +	if (head->mapping)
> +		return;
> +
> +	head->mapping = f_mapping;
> +	head->index = linear_page_index(vmf->vma,
> +			ALIGN(vmf->address, fault_size));
> +}

Should this stuff be setup before doing vmf_insert_pfn_XX?

In normal cases the page should be returned in the vmf and populated
to the page tables by the core code after all this is done. 

dax can't do that because of the refcount mess, but I would think the
basic ordering should be the same.

Jason