I didn't spot any issues with this nice clean up so:
Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx>
Dan Williams <dan.j.williams@xxxxxxxxx> writes:
> Now that fsdax DMA-idle detection no longer depends on catching
> transitions of page->_refcount to 1, and all users of pgmap pages get
> access to them via pgmap_request_folios(), remove
> put_devmap_managed_page_refs() and associated infrastructure. This
> includes the pgmap references taken at the beginning of time for each
> page because those @pgmap references are now arbitrated via
> pgmap_request_folios().
>
> 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>
> ---
> include/linux/mm.h | 30 ------------------------------
> mm/gup.c | 6 ++----
> mm/memremap.c | 38 --------------------------------------
> mm/swap.c | 2 --
> 4 files changed, 2 insertions(+), 74 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8bbcccbc5565..c63dfc804f1e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1082,30 +1082,6 @@ vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf);
> * back into memory.
> */
>
> -#if defined(CONFIG_ZONE_DEVICE) && defined(CONFIG_FS_DAX)
> -DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
> -
> -bool __put_devmap_managed_page_refs(struct page *page, int refs);
> -static inline bool put_devmap_managed_page_refs(struct page *page, int refs)
> -{
> - if (!static_branch_unlikely(&devmap_managed_key))
> - return false;
> - if (!is_zone_device_page(page))
> - return false;
> - return __put_devmap_managed_page_refs(page, refs);
> -}
> -#else /* CONFIG_ZONE_DEVICE && CONFIG_FS_DAX */
> -static inline bool put_devmap_managed_page_refs(struct page *page, int refs)
> -{
> - return false;
> -}
> -#endif /* CONFIG_ZONE_DEVICE && CONFIG_FS_DAX */
> -
> -static inline bool put_devmap_managed_page(struct page *page)
> -{
> - return put_devmap_managed_page_refs(page, 1);
> -}
> -
> /* 127: arbitrary random number, small enough to assemble well */
> #define folio_ref_zero_or_close_to_overflow(folio) \
> ((unsigned int) folio_ref_count(folio) + 127u <= 127u)
> @@ -1202,12 +1178,6 @@ static inline void put_page(struct page *page)
> {
> struct folio *folio = page_folio(page);
>
> - /*
> - * For some devmap managed pages we need to catch refcount transition
> - * from 2 to 1:
> - */
> - if (put_devmap_managed_page(&folio->page))
> - return;
> folio_put(folio);
> }
>
> diff --git a/mm/gup.c b/mm/gup.c
> index ce00a4c40da8..e49b1f46faa5 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -87,8 +87,7 @@ static inline struct folio *try_get_folio(struct page *page, int refs)
> * belongs to this folio.
> */
> if (unlikely(page_folio(page) != folio)) {
> - if (!put_devmap_managed_page_refs(&folio->page, refs))
> - folio_put_refs(folio, refs);
> + folio_put_refs(folio, refs);
> goto retry;
> }
>
> @@ -184,8 +183,7 @@ static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
> refs *= GUP_PIN_COUNTING_BIAS;
> }
>
> - if (!put_devmap_managed_page_refs(&folio->page, refs))
> - folio_put_refs(folio, refs);
> + folio_put_refs(folio, refs);
> }
>
> /**
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 368ff41c560b..53fe30bb79bb 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -94,19 +94,6 @@ bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn)
> return false;
> }
>
> -static unsigned long pfn_end(struct dev_pagemap *pgmap, int range_id)
> -{
> - const struct range *range = &pgmap->ranges[range_id];
> -
> - return (range->start + range_len(range)) >> PAGE_SHIFT;
> -}
> -
> -static unsigned long pfn_len(struct dev_pagemap *pgmap, unsigned long range_id)
> -{
> - return (pfn_end(pgmap, range_id) -
> - pfn_first(pgmap, range_id)) >> pgmap->vmemmap_shift;
> -}
> -
> static void pageunmap_range(struct dev_pagemap *pgmap, int range_id)
> {
> struct range *range = &pgmap->ranges[range_id];
> @@ -138,10 +125,6 @@ void memunmap_pages(struct dev_pagemap *pgmap)
> int i;
>
> percpu_ref_kill(&pgmap->ref);
> - if (pgmap->type != MEMORY_DEVICE_PRIVATE &&
> - pgmap->type != MEMORY_DEVICE_COHERENT)
> - for (i = 0; i < pgmap->nr_range; i++)
> - percpu_ref_put_many(&pgmap->ref, pfn_len(pgmap, i));
>
> wait_for_completion(&pgmap->done);
>
> @@ -267,9 +250,6 @@ static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
> memmap_init_zone_device(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
> PHYS_PFN(range->start),
> PHYS_PFN(range_len(range)), pgmap);
> - if (pgmap->type != MEMORY_DEVICE_PRIVATE &&
> - pgmap->type != MEMORY_DEVICE_COHERENT)
> - percpu_ref_get_many(&pgmap->ref, pfn_len(pgmap, range_id));
> return 0;
>
> err_add_memory:
> @@ -584,21 +564,3 @@ void pgmap_release_folios(struct folio *folio, int nr_folios)
> for (iter = folio, i = 0; i < nr_folios; iter = folio_next(folio), i++)
> folio_put(iter);
> }
> -
> -#ifdef CONFIG_FS_DAX
> -bool __put_devmap_managed_page_refs(struct page *page, int refs)
> -{
> - if (page->pgmap->type != MEMORY_DEVICE_FS_DAX)
> - return false;
> -
> - /*
> - * fsdax page refcounts are 1-based, rather than 0-based: if
> - * refcount is 1, then the page is free and the refcount is
> - * stable because nobody holds a reference on the page.
> - */
> - if (page_ref_sub_return(page, refs) == 1)
> - wake_up_var(page);
> - return true;
> -}
> -EXPORT_SYMBOL(__put_devmap_managed_page_refs);
> -#endif /* CONFIG_FS_DAX */
> diff --git a/mm/swap.c b/mm/swap.c
> index 955930f41d20..0742b84fbf17 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -1003,8 +1003,6 @@ void release_pages(struct page **pages, int nr)
> unlock_page_lruvec_irqrestore(lruvec, flags);
> lruvec = NULL;
> }
> - if (put_devmap_managed_page(&folio->page))
> - continue;
> if (folio_put_testzero(folio))
> free_zone_device_page(&folio->page);
> continue;
