Re: [PATCH mm-unstable v2 1/5] mm: consolidate anonymous folio PTE mapping into helpers

["David Hildenbrand (Arm)" <david@kernel.org>]

On 2/26/26 02:29, Nico Pache wrote:
> The anonymous page fault handler in do_anonymous_page() open-codes the
> sequence to map a newly allocated anonymous folio at the PTE level:
> 	- construct the PTE entry
> 	- add rmap
> 	- add to LRU
> 	- set the PTEs
> 	- update the MMU cache.
> 
> Introduce a two helpers to consolidate this duplicated logic, mirroring the
> existing map_anon_folio_pmd_nopf() pattern for PMD-level mappings:
> 
> 	map_anon_folio_pte_nopf(): constructs the PTE entry, takes folio
> 	references, adds anon rmap and LRU. This function also handles the
> 	uffd_wp that can occur in the pf variant.
> 
> 	map_anon_folio_pte_pf(): extends the nopf variant to handle MM_ANONPAGES
> 	counter updates, and mTHP fault allocation statistics for the page fault
> 	path.
> 
> The zero-page read path in do_anonymous_page() is also untangled from the
> shared setpte label, since it does not allocate a folio and should not
> share the same mapping sequence as the write path. Make nr_pages = 1
> rather than relying on the variable. This makes it more clear that we
> are operating on the zero page only.
> 
> This refactoring will also help reduce code duplication between mm/memory.c
> and mm/khugepaged.c, and provides a clean API for PTE-level anonymous folio
> mapping that can be reused by future callers.
> 
> Signed-off-by: Nico Pache <npache@redhat.com>
> ---
>  include/linux/mm.h |  4 ++++
>  mm/memory.c        | 59 +++++++++++++++++++++++++++++++---------------
>  2 files changed, 44 insertions(+), 19 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 13336340612e..3ebf143c7502 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4901,4 +4901,8 @@ static inline bool snapshot_page_is_faithful(const struct page_snapshot *ps)
>  
>  void snapshot_page(struct page_snapshot *ps, const struct page *page);
>  
> +void map_anon_folio_pte_nopf(struct folio *folio, pte_t *pte,
> +		struct vm_area_struct *vma, unsigned long addr,
> +		bool uffd_wp);
> +
>  #endif /* _LINUX_MM_H */
> diff --git a/mm/memory.c b/mm/memory.c
> index 9385842c3503..a1a364e1fdcd 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5189,6 +5189,36 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
>  	return folio_prealloc(vma->vm_mm, vma, vmf->address, true);
>  }
>  
> +void map_anon_folio_pte_nopf(struct folio *folio, pte_t *pte,
> +		struct vm_area_struct *vma, unsigned long addr,
> +		bool uffd_wp)
> +{
> +	unsigned int nr_pages = folio_nr_pages(folio);
> +	pte_t entry = folio_mk_pte(folio, vma->vm_page_prot);
> +
> +	entry = pte_sw_mkyoung(entry);
> +
> +	if (vma->vm_flags & VM_WRITE)
> +		entry = pte_mkwrite(pte_mkdirty(entry), vma);
> +	if (uffd_wp)
> +		entry = pte_mkuffd_wp(entry);
> +
> +	folio_ref_add(folio, nr_pages - 1);
> +	folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE);
> +	folio_add_lru_vma(folio, vma);
> +	set_ptes(vma->vm_mm, addr, pte, entry, nr_pages);
> +	update_mmu_cache_range(NULL, vma, addr, pte, nr_pages);
> +}
> +
> +static void map_anon_folio_pte_pf(struct folio *folio, pte_t *pte,
> +		struct vm_area_struct *vma, unsigned long addr,
> +		unsigned int nr_pages, bool uffd_wp)
> +{
> +	map_anon_folio_pte_nopf(folio, pte, vma, addr, uffd_wp);
> +	add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages);
> +	count_mthp_stat(folio_order(folio), MTHP_STAT_ANON_FAULT_ALLOC);
> +}

One thing:

You can also void passing in "nr_pages" here, especially when you query
the order below, and simply do

unsigned int order = folio_order(folio);

map_anon_folio_pte_nopf(folio, pte, vma, addr, uffd_wp);
add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1U << order);
count_mthp_stat(order, MTHP_STAT_ANON_FAULT_ALLOC);


Apart from that

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David