Re: [RFC PATCH 02/25] mm/zsmalloc: add utility functions for zsdesc

[Mike Rapoport <rppt@kernel.org>]

On Mon, Feb 20, 2023 at 01:21:55PM +0000, Hyeonggon Yoo wrote:
> Introduce utility functions for zsdesc to avoid directly accessing fields
> of struct page.
> 
> zsdesc_page() is defined this way to preserve constness. page_zsdesc() does

I'd suggest "zsdesc_page() is defined with _Generic to preserve constness"
and add a line break before page_zsdesc().

> not call compound_head() because zsdesc is always a base page.
> 
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> ---
>  mm/zsmalloc.c | 120 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 118 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index e2e34992c439..4af9f87cafb7 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -332,6 +332,124 @@ ZSDESC_MATCH(_refcount, _refcount);
>  #undef ZSDESC_MATCH
>  static_assert(sizeof(struct zsdesc) <= sizeof(struct page));

I didn't do through check if it's feasible, but I think it would be better
to add helpers along with their usage.

For instance, move definition of zdesc_page() and page_zsdesc() to
"mm/zsmalloc: replace first_page to first_zsdesc in struct zspage" and so
on.
  
> +#define zsdesc_page(zdesc) (_Generic((zdesc),				\
> +		const struct zsdesc *:	(const struct page *)zdesc,	\
> +		struct zsdesc *:	(struct page *)zdesc))
> +
> +static inline struct zsdesc *page_zsdesc(struct page *page)
> +{
> +	return (struct zsdesc *)page;
> +}
> +
> +static inline unsigned long zsdesc_pfn(const struct zsdesc *zsdesc)
> +{
> +	return page_to_pfn(zsdesc_page(zsdesc));
> +}
> +
> +static inline struct zsdesc *pfn_zsdesc(unsigned long pfn)
> +{
> +	return page_zsdesc(pfn_to_page(pfn));
> +}
> +
> +static inline struct zspage *zsdesc_zspage(const struct zsdesc *zsdesc)
> +{
> +	return (struct zspage *)page_private(zsdesc_page(zsdesc));
> +}
> +
> +static inline int trylock_zsdesc(struct zsdesc *zsdesc)
> +{
> +	return trylock_page(zsdesc_page(zsdesc));
> +}
> +
> +static inline void unlock_zsdesc(struct zsdesc *zsdesc)
> +{
> +	return unlock_page(zsdesc_page(zsdesc));
> +}
> +
> +static inline struct zone *zsdesc_zone(struct zsdesc *zsdesc)
> +{
> +	return page_zone(zsdesc_page(zsdesc));
> +}
> +
> +static inline void wait_on_zsdesc_locked(struct zsdesc *zsdesc)
> +{
> +	wait_on_page_locked(zsdesc_page(zsdesc));
> +}
> +
> +static inline void zsdesc_get(struct zsdesc *zsdesc)
> +{
> +	struct folio *folio = (struct folio *)zsdesc;
> +
> +	folio_get(folio);
> +}
> +
> +static inline void zsdesc_put(struct zsdesc *zsdesc)
> +{
> +	struct folio *folio = (struct folio *)zsdesc;
> +
> +	folio_put(folio);
> +}
> +
> +static inline void *zsdesc_kmap_atomic(struct zsdesc *zsdesc)
> +{
> +	return kmap_atomic(zsdesc_page(zsdesc));
> +}
> +
> +static inline void zsdesc_set_zspage(struct zsdesc *zsdesc, struct zspage *zspage)
> +{
> +	set_page_private(zsdesc_page(zsdesc), (unsigned long)zspage);
> +}
> +
> +static inline void zsdesc_set_first(struct zsdesc *zsdesc)
> +{
> +	SetPagePrivate(zsdesc_page(zsdesc));
> +}
> +
> +static inline bool zsdesc_is_locked(struct zsdesc *zsdesc)
> +{
> +	return PageLocked(zsdesc_page(zsdesc));
> +}
> +
> +static inline bool zsdesc_is_isolated(struct zsdesc *zsdesc)
> +{
> +	return PageIsolated(zsdesc_page(zsdesc));
> +}
> +
> +static inline void zsdesc_inc_zone_page_state(struct zsdesc *zsdesc)
> +{
> +	inc_zone_page_state(zsdesc_page(zsdesc), NR_ZSPAGES);
> +}
> +
> +static inline void zsdesc_dec_zone_page_state(struct zsdesc *zsdesc)
> +{
> +	dec_zone_page_state(zsdesc_page(zsdesc), NR_ZSPAGES);
> +}
> +
> +static inline struct zsdesc *alloc_zsdesc(gfp_t gfp)
> +{
> +	struct page *page = alloc_page(gfp);
> +
> +	zsdesc_inc_zone_page_state(page_zsdesc(page));
> +	return page_zsdesc(page);
> +}
> +
> +static inline void free_zsdesc(struct zsdesc *zsdesc)
> +{
> +	struct page *page = zsdesc_page(zsdesc);
> +
> +	zsdesc_dec_zone_page_state(page_zsdesc(page));
> +	__free_page(page);
> +}
> +
> +static const struct movable_operations zsmalloc_mops;
> +
> +static inline void zsdesc_set_movable(struct zsdesc *zsdesc)
> +{
> +	struct page *page = zsdesc_page(zsdesc);
> +
> +	__SetPageMovable(page, &zsmalloc_mops);
> +}
> +
>  /* huge object: pages_per_zspage == 1 && maxobj_per_zspage == 1 */
>  static void SetZsHugePage(struct zspage *zspage)
>  {
> @@ -2012,8 +2130,6 @@ static void dec_zspage_isolation(struct zspage *zspage)
>  	zspage->isolated--;
>  }
>  
> -static const struct movable_operations zsmalloc_mops;
> -
>  static void replace_sub_page(struct size_class *class, struct zspage *zspage,
>  				struct page *newpage, struct page *oldpage)
>  {
> -- 
> 2.25.1
> 
> 

-- 
Sincerely yours,
Mike.