Re: [PATCH 01/28] mm: Remove folio_pincount_ptr() and head_compound_pincount()

[John Hubbard <jhubbard@nvidia.com>]

On 1/11/23 06:28, Matthew Wilcox (Oracle) wrote:
> We can use folio->_pincount directly, since all users are guarded by
> tests of compound/large.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>   Documentation/core-api/pin_user_pages.rst | 29 +++++++++++------------
>   include/linux/mm.h                        | 14 ++---------
>   include/linux/mm_types.h                  |  5 ----
>   mm/debug.c                                |  4 ++--
>   mm/gup.c                                  |  8 +++----
>   mm/huge_memory.c                          |  4 ++--
>   mm/hugetlb.c                              |  4 ++--
>   mm/page_alloc.c                           |  9 ++++---
>   8 files changed, 32 insertions(+), 45 deletions(-)

Looks very nice, just a couple of questions about casts, below.

...

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4d9afa1048ea..d1e5ec875fd0 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -775,11 +775,13 @@ void free_compound_page(struct page *page)
>   
>   static void prep_compound_head(struct page *page, unsigned int order)
>   {
> +	struct folio *folio = (struct folio *)page;

Casting, eh? I wonder if prep_compound_head() should just take a folio?
There are only a few callers of that.

> +
>   	set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
>   	set_compound_order(page, order);
>   	atomic_set(compound_mapcount_ptr(page), -1);
>   	atomic_set(subpages_mapcount_ptr(page), 0);
> -	atomic_set(compound_pincount_ptr(page), 0);
> +	atomic_set(&folio->_pincount, 0);
>   }
>   
>   static void prep_compound_tail(struct page *head, int tail_idx)
> @@ -1291,6 +1293,7 @@ static inline bool free_page_is_bad(struct page *page)
>   
>   static int free_tail_pages_check(struct page *head_page, struct page *page)
>   {
> +	struct folio *folio = (struct folio *)head_page;

Similar to above: should the function just accept a folio instead of a
page?

Anyway, the patch as-is is good, and those points could be follow-up
changes if they are done, so either way, please feel free to add:


Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
-- 
John Hubbard
NVIDIA