Re: [PATCH v3 4/4] mm/zsmalloc: document free_zspage helper variants

[Nhat Pham]

On Fri, Jun 5, 2026 at 1:43 AM Wenchao Hao <haowenchao22@xxxxxxxxx> wrote:
>
> From: Wenchao Hao <haowenchao@xxxxxxxxxx>
>
> After splitting __free_zspage() into a lockless core and a wrapper that
> does the class-stat bookkeeping, three similarly-named helpers coexist:
> free_zspage / __free_zspage / __free_zspage_lockless.
>
> Add a comment block above them describing what each does and where it
> is used, so the names are not easy to confuse.
>
> No functional change.
>
> Suggested-by: Nhat Pham <nphamcs@xxxxxxxxx>
> Signed-off-by: Wenchao Hao <haowenchao@xxxxxxxxxx>

I think it LGTM, but I'll let the zsmalloc maintainers have their say :)

Feel free to add:
Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>



> ---
>  mm/zsmalloc.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 2ecdf79cea03..9f588b63ec0d 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -856,6 +856,21 @@ static int trylock_zspage(struct zspage *zspage)
>         return 0;
>  }
>
> +/*
> + * Three free helpers, kept apart here:
> + *
> + * __free_zspage_lockless(): bare core; walks zpdescs and returns pages
> + *   to the buddy allocator.  Caller owns all zpdesc locks and has
> + *   removed the zspage from its class list.  Used by zs_free() outside
> + *   class->lock so the buddy-side work does not stall the class.
> + *
> + * __free_zspage(): __free_zspage_lockless() + per-class accounting,
> + *   under class->lock.  Used by async_free_zspage().

nit: maybe a short note on when async_free_zspage is needed?

(IIUC, only when trylock_zspage() fails in zs_free(), correct?)

> + *
> + * free_zspage(): full wrapper - trylock zpdescs, remove from class
> + *   list, call __free_zspage(); kicks deferred free on contention.
> + *   Used by compaction.
> + */
>  static inline void __free_zspage_lockless(struct zs_pool *pool, struct zspage *zspage)
>  {
>         struct zpdesc *zpdesc, *next;
> --
> 2.34.1
>