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

["Yin, Fengwei" <fengwei.yin@intel.com>]

On 1/31/2023 3:24 PM, Huang, Ying wrote:
> 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.
Oops. This should be used in while (page++, ++i < count);
Maybe this line can be removed if we are sure the range is not out of
folio size? Thanks.

Regards
Yin, Fengwei

> 
> 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