On Mon, Dec 16, 2024 at 03:53:56PM +0000, Matthew Wilcox (Oracle) wrote:
> Convert from pfn to folio instead of page and use those folios
> throughout to avoid accesses to page->index and page->mapping.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> fs/dax.c | 53 +++++++++++++++++++++++++++--------------------------
> 1 file changed, 27 insertions(+), 26 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 21b47402b3dc..972febc6fb9d 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -320,38 +320,39 @@ static unsigned long dax_end_pfn(void *entry)
> for (pfn = dax_to_pfn(entry); \
> pfn < dax_end_pfn(entry); pfn++)
>
> -static inline bool dax_page_is_shared(struct page *page)
> +static inline bool dax_folio_is_shared(struct folio *folio)
> {
> - return page->mapping == PAGE_MAPPING_DAX_SHARED;
> + return folio->mapping == PAGE_MAPPING_DAX_SHARED;
This will conflict with my series which introduces compound ZONE_DEVICE
pages to free up a PTE bit and allow FS DAX pages to be refcounted
normally. The main change is here -
https://lore.kernel.org/ linux-mm/39a896451e59b735f205e34da5510ead5e4cd47d.1732239628.git-series.apopple@xxxxxxxxxx/
I'm hoping we can get that in linux-next "soon".
> }
>
> /*
> - * Set the page->mapping with PAGE_MAPPING_DAX_SHARED flag, increase the
> + * Set the folio->mapping with PAGE_MAPPING_DAX_SHARED flag, increase the
> * refcount.
> */
> -static inline void dax_page_share_get(struct page *page)
> +static inline void dax_folio_share_get(struct folio *folio)
> {
> - if (page->mapping != PAGE_MAPPING_DAX_SHARED) {
> + if (folio->mapping != PAGE_MAPPING_DAX_SHARED) {
> /*
> * Reset the index if the page was already mapped
> * regularly before.
> */
> - if (page->mapping)
> - page->share = 1;
> - page->mapping = PAGE_MAPPING_DAX_SHARED;
> + if (folio->mapping)
> + folio->page.share = 1;
It also moves the share accounting to the folio as well so we could remove the
whole page->index/share union once that's merged.
> + folio->mapping = PAGE_MAPPING_DAX_SHARED;
> }
> - page->share++;
> + folio->page.share++;
> }
>
> -static inline unsigned long dax_page_share_put(struct page *page)
> +static inline unsigned long dax_folio_share_put(struct folio *folio)
> {
> - return --page->share;
> + return --folio->page.share;
> }
>
> /*
> - * When it is called in dax_insert_entry(), the shared flag will indicate that
> - * whether this entry is shared by multiple files. If so, set the page->mapping
> - * PAGE_MAPPING_DAX_SHARED, and use page->share as refcount.
> + * When it is called in dax_insert_entry(), the shared flag will indicate
> + * that whether this entry is shared by multiple files. If so, set
> + * the folio->mapping PAGE_MAPPING_DAX_SHARED, and use page->share
> + * as refcount.
> */
> static void dax_associate_entry(void *entry, struct address_space *mapping,
> struct vm_area_struct *vma, unsigned long address, bool shared)
> @@ -364,14 +365,14 @@ static void dax_associate_entry(void *entry, struct address_space *mapping,
>
> index = linear_page_index(vma, address & ~(size - 1));
> for_each_mapped_pfn(entry, pfn) {
> - struct page *page = pfn_to_page(pfn);
> + struct folio *folio = pfn_folio(pfn);
>
> if (shared) {
> - dax_page_share_get(page);
> + dax_folio_share_get(folio);
> } else {
> - WARN_ON_ONCE(page->mapping);
> - page->mapping = mapping;
> - page->index = index + i++;
> + WARN_ON_ONCE(folio->mapping);
> + folio->mapping = mapping;
> + folio->index = index + i++;
> }
> }
> }
> @@ -385,17 +386,17 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
> return;
>
> for_each_mapped_pfn(entry, pfn) {
> - struct page *page = pfn_to_page(pfn);
> + struct folio *folio = pfn_folio(pfn);
>
> - WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
> - if (dax_page_is_shared(page)) {
> + WARN_ON_ONCE(trunc && folio_ref_count(folio) > 1);
> + if (dax_folio_is_shared(folio)) {
> /* keep the shared flag if this page is still shared */
> - if (dax_page_share_put(page) > 0)
> + if (dax_folio_share_put(folio) > 0)
> continue;
> } else
> - WARN_ON_ONCE(page->mapping && page->mapping != mapping);
> - page->mapping = NULL;
> - page->index = 0;
> + WARN_ON_ONCE(folio->mapping && folio->mapping != mapping);
> + folio->mapping = NULL;
> + folio->index = 0;
> }
> }
>
> --
> 2.45.2
>
>
