Re: [RFC PATCH 3/5] rmap: add page_add_file_rmap_range()

["Huang, Ying" <ying.huang@intel.com>]

Yin Fengwei <fengwei.yin@intel.com> writes:

> page_add_file_rmap_range() allows to add specific range of
> large folio rmap.
>
> Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
> ---
>  include/linux/rmap.h |  2 ++
>  mm/rmap.c            | 70 ++++++++++++++++++++++++++++----------------
>  2 files changed, 46 insertions(+), 26 deletions(-)
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index a6bd1f0a183d..063e0addcbf8 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -198,6 +198,8 @@ void folio_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
>  		unsigned long address);
>  void page_add_file_rmap(struct page *, struct vm_area_struct *,
>  		bool compound);
> +void page_add_file_rmap_range(struct folio *, struct page *, int len,
> +	struct vm_area_struct *, bool compound);
>  void page_remove_rmap(struct page *, struct vm_area_struct *,
>  		bool compound);
>  
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 948ca17a96ad..cc7fe3010330 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1301,40 +1301,19 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
>  	__page_set_anon_rmap(folio, &folio->page, vma, address, 1);
>  }
>  
> -/**
> - * page_add_file_rmap - add pte mapping to a file page
> - * @page:	the page to add the mapping to
> - * @vma:	the vm area in which the mapping is added
> - * @compound:	charge the page as compound or small page
> - *
> - * The caller needs to hold the pte lock.
> - */
> -void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
> -		bool compound)
> +void page_add_file_rmap_range(struct folio *folio, struct page *page, int len,
> +	struct vm_area_struct *vma, bool compound)
>  {
> -	struct folio *folio = page_folio(page);
>  	atomic_t *mapped = &folio->_nr_pages_mapped;
> -	int nr = 0, nr_pmdmapped = 0;
> +	int nr = 0, nr_pmdmapped = 0, nr_pages = folio_nr_pages(folio);
>  	bool first;
>  
> -	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
> -
> -	/* Is page being mapped by PTE? Is this its first map to be added? */
> -	if (likely(!compound)) {
> -		first = atomic_inc_and_test(&page->_mapcount);
> -		nr = first;
> -		if (first && folio_test_large(folio)) {
> -			nr = atomic_inc_return_relaxed(mapped);
> -			nr = (nr < COMPOUND_MAPPED);
> -		}
> -	} else if (folio_test_pmd_mappable(folio)) {
> -		/* That test is redundant: it's for safety or to optimize out */
> -
> +	if (compound) {
>  		first = atomic_inc_and_test(&folio->_entire_mapcount);
>  		if (first) {
>  			nr = atomic_add_return_relaxed(COMPOUND_MAPPED, mapped);
>  			if (likely(nr < COMPOUND_MAPPED + COMPOUND_MAPPED)) {
> -				nr_pmdmapped = folio_nr_pages(folio);
> +				nr_pmdmapped = nr_pages;
>  				nr = nr_pmdmapped - (nr & FOLIO_PAGES_MAPPED);
>  				/* Raced ahead of a remove and another add? */
>  				if (unlikely(nr < 0))
> @@ -1344,6 +1323,20 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>  				nr = 0;
>  			}
>  		}
> +	} else {
> +		int i = 0, new_mapped = 0, count;
> +
> +		count = min_t(int, len, nr_pages - folio_page_idx(folio, page));

It appears that count isn't used after assignment.

Best Regards,
Huang, Ying

> +		do {
> +			first = atomic_inc_and_test(&page->_mapcount);
> +			new_mapped = first;
> +			if (first && folio_test_large(folio)) {
> +				new_mapped = atomic_inc_return_relaxed(mapped);
> +				new_mapped = (new_mapped < COMPOUND_MAPPED);
> +			}
> +			if  (new_mapped)
> +				nr++;
> +		} while (page++, ++i < len);
>  	}
>  
>  	if (nr_pmdmapped)
> @@ -1355,6 +1348,31 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>  	mlock_vma_folio(folio, vma, compound);
>  }
>  
> +/**
> + * page_add_file_rmap - add pte mapping to a file page
> + * @page:	the page to add the mapping to
> + * @vma:	the vm area in which the mapping is added
> + * @compound:	charge the page as compound or small page
> + *
> + * The caller needs to hold the pte lock.
> + */
> +void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
> +		bool compound)
> +{
> +	struct folio *folio = page_folio(page);
> +	int nr_pages;
> +
> +	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
> +
> +	if (likely(!compound))
> +		nr_pages = 1;
> +	else
> +		nr_pages = folio_nr_pages(folio);
> +
> +	page_add_file_rmap_range(folio, page, nr_pages, vma, compound);
> +}
> +
>  /**
>   * page_remove_rmap - take down pte mapping from a page
>   * @page:	page to remove mapping from