Re: [PATCH v2 13/18] dax: Prep mapping helpers for compound pages

Jason Gunthorpe
2022-09-21T14:06:17Z

On Thu, Sep 15, 2022 at 08:36:25PM -0700, Dan Williams wrote:
> In preparation for device-dax to use the same mapping machinery as
> fsdax, add support for device-dax compound pages.
>
> Presently this is handled by dax_set_mapping() which is careful to only
> update page->mapping for head pages. However, it does that by looking at
> properties in the 'struct dev_dax' instance associated with the page.
> Switch to just checking PageHead() directly in the functions that
> iterate over pages in a large mapping.
>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Jan Kara <jack@suse.cz>
> Cc: "Darrick J. Wong" <djwong@kernel.org>
> Cc: Jason Gunthorpe <jgg@nvidia.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> drivers/dax/Kconfig | 1 +
> drivers/dax/mapping.c | 16 ++++++++++++++++
> 2 files changed, 17 insertions(+)
>
> diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
> index 205e9dda8928..2eddd32c51f4 100644
> --- a/drivers/dax/Kconfig
> +++ b/drivers/dax/Kconfig
> @@ -9,6 +9,7 @@ if DAX
> config DEV_DAX
> tristate "Device DAX: direct access mapping device"
> depends on TRANSPARENT_HUGEPAGE
> + depends on !FS_DAX_LIMITED
> help
> Support raw access to differentiated (persistence, bandwidth,
> latency...) memory via an mmap(2) capable character
> diff --git a/drivers/dax/mapping.c b/drivers/dax/mapping.c
> index 70576aa02148..5d4b9601f183 100644
> --- a/drivers/dax/mapping.c
> +++ b/drivers/dax/mapping.c
> @@ -345,6 +345,8 @@ static vm_fault_t dax_associate_entry(void *entry,
> for_each_mapped_pfn(entry, pfn) {
> struct page *page = pfn_to_page(pfn);
>
> + page = compound_head(page);

I feel like the word folio is need here.. pfn_to_folio() or something?

At the very least we should have a struct folio after doing the
compound_head, right?

Jason