The DEVICE_PRIVATE/COHERENT changes look good to me so feel free to add:
Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx>
Dan Williams <dan.j.williams@xxxxxxxxx> writes:
> The initial memremap_pages() implementation inherited the
> __init_single_page() default of pages starting life with an elevated
> reference count. This originally allowed for the page->pgmap pointer to
> alias with the storage for page->lru since a page was only allowed to be
> on an lru list when its reference count was zero.
>
> Since then, 'struct page' definition cleanups have arranged for
> dedicated space for the ZONE_DEVICE page metadata, the
> MEMORY_DEVICE_{PRIVATE,COHERENT} work has arranged for the 1 -> 0
> page->_refcount transition to route the page to free_zone_device_page()
> and not the core-mm page-free, and MEMORY_DEVICE_{PRIVATE,COHERENT} now
> arranges for its ZONE_DEVICE pages to start at _refcount 0. With those
> cleanups in place and with filesystem-dax and device-dax now converted
> to take and drop references at map and truncate time, it is possible to
> start MEMORY_DEVICE_FS_DAX and MEMORY_DEVICE_GENERIC reference counts at
> 0 as well.
>
> This conversion also unifies all @pgmap accounting to be relative to
> pgmap_request_folio() and the paired folio_put() calls for those
> requested folios. This allows pgmap_release_folios() to be simplified to
> just a folio_put() helper.
>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: "Darrick J. Wong" <djwong@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Alistair Popple <apopple@xxxxxxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
> drivers/dax/mapping.c | 2 +-
> include/linux/dax.h | 2 +-
> include/linux/memremap.h | 6 ++----
> mm/memremap.c | 36 ++++++++++++++++--------------------
> mm/page_alloc.c | 9 +--------
> 5 files changed, 21 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/dax/mapping.c b/drivers/dax/mapping.c
> index 07caaa23d476..ca06f2515644 100644
> --- a/drivers/dax/mapping.c
> +++ b/drivers/dax/mapping.c
> @@ -691,7 +691,7 @@ static struct page *dax_zap_pages(struct xa_state *xas, void *entry)
>
> dax_for_each_folio(entry, folio, i) {
> if (zap)
> - pgmap_release_folios(folio_pgmap(folio), folio, 1);
> + pgmap_release_folios(folio, 1);
> if (!ret && !dax_folio_idle(folio))
> ret = folio_page(folio, 0);
> }
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index f2fbb5746ffa..f4fc37933fc2 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -235,7 +235,7 @@ static inline void dax_unlock_mapping_entry(struct address_space *mapping,
> */
> static inline bool dax_page_idle(struct page *page)
> {
> - return page_ref_count(page) == 1;
> + return page_ref_count(page) == 0;
> }
>
> static inline bool dax_folio_idle(struct folio *folio)
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 3fb3809d71f3..ddb196ae0696 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -195,8 +195,7 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
> struct dev_pagemap *pgmap);
> bool pgmap_request_folios(struct dev_pagemap *pgmap, struct folio *folio,
> int nr_folios);
> -void pgmap_release_folios(struct dev_pagemap *pgmap, struct folio *folio,
> - int nr_folios);
> +void pgmap_release_folios(struct folio *folio, int nr_folios);
> bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn);
>
> unsigned long vmem_altmap_offset(struct vmem_altmap *altmap);
> @@ -238,8 +237,7 @@ static inline bool pgmap_request_folios(struct dev_pagemap *pgmap,
> return false;
> }
>
> -static inline void pgmap_release_folios(struct dev_pagemap *pgmap,
> - struct folio *folio, int nr_folios)
> +static inline void pgmap_release_folios(struct folio *folio, int nr_folios)
> {
> }
>
> diff --git a/mm/memremap.c b/mm/memremap.c
> index c46e700f5245..368ff41c560b 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -469,8 +469,10 @@ EXPORT_SYMBOL_GPL(get_dev_pagemap);
>
> void free_zone_device_page(struct page *page)
> {
> - if (WARN_ON_ONCE(!page->pgmap->ops || !page->pgmap->ops->page_free))
> - return;
> + struct dev_pagemap *pgmap = page->pgmap;
> +
> + /* wake filesystem 'break dax layouts' waiters */
> + wake_up_var(page);
>
> mem_cgroup_uncharge(page_folio(page));
>
> @@ -505,17 +507,9 @@ void free_zone_device_page(struct page *page)
> * to clear page->mapping.
> */
> page->mapping = NULL;
> - page->pgmap->ops->page_free(page);
> -
> - if (page->pgmap->type != MEMORY_DEVICE_PRIVATE &&
> - page->pgmap->type != MEMORY_DEVICE_COHERENT)
> - /*
> - * Reset the page count to 1 to prepare for handing out the page
> - * again.
> - */
> - set_page_count(page, 1);
> - else
> - put_dev_pagemap(page->pgmap);
> + if (pgmap->ops && pgmap->ops->page_free)
> + pgmap->ops->page_free(page);
> + put_dev_pagemap(page->pgmap);
> }
>
> static bool folio_span_valid(struct dev_pagemap *pgmap, struct folio *folio,
> @@ -576,17 +570,19 @@ bool pgmap_request_folios(struct dev_pagemap *pgmap, struct folio *folio,
> }
> EXPORT_SYMBOL_GPL(pgmap_request_folios);
>
> -void pgmap_release_folios(struct dev_pagemap *pgmap, struct folio *folio, int nr_folios)
> +/*
> + * A symmetric helper to undo the page references acquired by
> + * pgmap_request_folios(), but the caller can also just arrange
> + * folio_put() on all the folios it acquired previously for the same
> + * effect.
> + */
> +void pgmap_release_folios(struct folio *folio, int nr_folios)
> {
> struct folio *iter;
> int i;
>
> - for (iter = folio, i = 0; i < nr_folios; iter = folio_next(iter), i++) {
> - if (!put_devmap_managed_page(&iter->page))
> - folio_put(iter);
> - if (!folio_ref_count(iter))
> - put_dev_pagemap(pgmap);
> - }
> + for (iter = folio, i = 0; i < nr_folios; iter = folio_next(folio), i++)
> + folio_put(iter);
> }
>
> #ifdef CONFIG_FS_DAX
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8e9b7f08a32c..e35d1eb3308d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6787,6 +6787,7 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
> {
>
> __init_single_page(page, pfn, zone_idx, nid);
> + set_page_count(page, 0);
>
> /*
> * Mark page reserved as it will need to wait for onlining
> @@ -6819,14 +6820,6 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
> set_pageblock_migratetype(page, MIGRATE_MOVABLE);
> cond_resched();
> }
> -
> - /*
> - * ZONE_DEVICE pages are released directly to the driver page allocator
> - * which will set the page count to 1 when allocating the page.
> - */
> - if (pgmap->type == MEMORY_DEVICE_PRIVATE ||
> - pgmap->type == MEMORY_DEVICE_COHERENT)
> - set_page_count(page, 0);
> }
>
> /*
