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

Dan Williams
2022-09-21T15:19:45Z

Jason Gunthorpe wrote:
> 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?

True, I can move this to the folio helpers.