Re: [PATCH v1 04/10] mm: Implement folio_add_new_anon_rmap_range()

Yin Fengwei
2023-06-28T02:17:06Z

On 6/27/23 15:08, Yu Zhao wrote:
> On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>
>> Like folio_add_new_anon_rmap() but batch-rmaps a range of pages
>> belonging to a folio, for effciency savings. All pages are accounted as
>> small pages.
>>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> ---
>> include/linux/rmap.h | 2 ++
>> mm/rmap.c | 43 +++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 45 insertions(+)
>>
>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
>> index a3825ce81102..15433a3d0cbf 100644
>> --- a/include/linux/rmap.h
>> +++ b/include/linux/rmap.h
>> @@ -196,6 +196,8 @@ void page_add_new_anon_rmap(struct page *, struct vm_area_struct *,
>> unsigned long address);
>> void folio_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
>> unsigned long address);
>> +void folio_add_new_anon_rmap_range(struct folio *folio, struct page *page,
>> + int nr, struct vm_area_struct *vma, unsigned long address);
>
> We should update folio_add_new_anon_rmap() to support large() &&
> !folio_test_pmd_mappable() folios instead.
>
> I double checked all places currently using folio_add_new_anon_rmap(),
> and as expected, none actually allocates large() &&
> !folio_test_pmd_mappable() and maps it one by one, which makes the
> cases simpler, i.e.,
> if (!large())
> // the existing basepage case
> else if (!folio_test_pmd_mappable())
> // our new case
> else
> // the existing THP case
I suppose we can merge the new case and existing THP case.

Regards
Yin, Fengwei

>
>> void page_add_file_rmap(struct page *, struct vm_area_struct *,
>> bool compound);
>> void folio_add_file_rmap_range(struct folio *, struct page *, unsigned int nr,
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index 1d8369549424..4050bcea7ae7 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1305,6 +1305,49 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
>> __page_set_anon_rmap(folio, &folio->page, vma, address, 1);
>> }
>>
>> +/**
>> + * folio_add_new_anon_rmap_range - Add mapping to a set of pages within a new
>> + * anonymous potentially large folio.
>> + * @folio: The folio containing the pages to be mapped
>> + * @page: First page in the folio to be mapped
>> + * @nr: Number of pages to be mapped
>> + * @vma: the vm area in which the mapping is added
>> + * @address: the user virtual address of the first page to be mapped
>> + *
>> + * Like folio_add_new_anon_rmap() but batch-maps a range of pages within a folio
>> + * using non-THP accounting. Like folio_add_new_anon_rmap(), the inc-and-test is
>> + * bypassed and the folio does not have to be locked. All pages in the folio are
>> + * individually accounted.
>> + *
>> + * As the folio is new, it's assumed to be mapped exclusively by a single
>> + * process.
>> + */
>> +void folio_add_new_anon_rmap_range(struct folio *folio, struct page *page,
>> + int nr, struct vm_area_struct *vma, unsigned long address)
>> +{
>> + int i;
>> +
>> + VM_BUG_ON_VMA(address < vma->vm_start ||
>> + address + (nr << PAGE_SHIFT) > vma->vm_end, vma);
>
> BTW, VM_BUG_ON* shouldn't be used in new code:
> Documentation/process/coding-style.rst