Re: [PATCH 03/10] slab: Add SL_private flag

[Harry Yoo <harry.yoo@oracle.com>]

On Fri, Jun 06, 2025 at 11:22:05PM +0100, Matthew Wilcox (Oracle) wrote:
> Give slab its own name for this flag.  Keep the PG_workingset alias
> information in one place.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---

nit: subject should be "slab: Add SL_partial flag"

Otherwise looks good to me.

Acked-by: Harry Yoo <harry.yoo@oracle.com>

-- 
Cheers,
Harry / Hyeonggon

>  mm/slab.h |  2 ++
>  mm/slub.c | 20 ++++++++------------
>  2 files changed, 10 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/slab.h b/mm/slab.h
> index a25f12244b6c..fca818011f7d 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -116,6 +116,7 @@ static_assert(IS_ALIGNED(offsetof(struct slab, freelist), sizeof(freelist_aba_t)
>  /**
>   * enum slab_flags - How the slab flags bits are used.
>   * @SL_locked: Is locked with slab_lock()
> + * @SL_partial: On the per-node partial list
>   *
>   * The slab flags share space with the page flags but some bits have
>   * different interpretations.  The high bits are used for information
> @@ -123,6 +124,7 @@ static_assert(IS_ALIGNED(offsetof(struct slab, freelist), sizeof(freelist_aba_t)
>   */
>  enum slab_flags {
>  	SL_locked,
> +	SL_partial = PG_workingset,	/* Historical reasons for this bit */
>  };
>  
>  /**
> diff --git a/mm/slub.c b/mm/slub.c
> index e9cbacee406d..804b39d06fa0 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -91,14 +91,14 @@
>   *   The partially empty slabs cached on the CPU partial list are used
>   *   for performance reasons, which speeds up the allocation process.
>   *   These slabs are not frozen, but are also exempt from list management,
> - *   by clearing the PG_workingset flag when moving out of the node
> + *   by clearing the SL_partial flag when moving out of the node
>   *   partial list. Please see __slab_free() for more details.
>   *
>   *   To sum up, the current scheme is:
> - *   - node partial slab: PG_Workingset && !frozen
> - *   - cpu partial slab: !PG_Workingset && !frozen
> - *   - cpu slab: !PG_Workingset && frozen
> - *   - full slab: !PG_Workingset && !frozen
> + *   - node partial slab: SL_partial && !frozen
> + *   - cpu partial slab: !SL_partial && !frozen
> + *   - cpu slab: !SL_partial && frozen
> + *   - full slab: !SL_partial && !frozen
>   *
>   *   list_lock
>   *
> @@ -2717,23 +2717,19 @@ static void discard_slab(struct kmem_cache *s, struct slab *slab)
>  	free_slab(s, slab);
>  }
>  
> -/*
> - * SLUB reuses PG_workingset bit to keep track of whether it's on
> - * the per-node partial list.
> - */
>  static inline bool slab_test_node_partial(const struct slab *slab)
>  {
> -	return folio_test_workingset(slab_folio(slab));
> +	return test_bit(SL_partial, &slab->flags);
>  }
>  
>  static inline void slab_set_node_partial(struct slab *slab)
>  {
> -	set_bit(PG_workingset, folio_flags(slab_folio(slab), 0));
> +	set_bit(SL_partial, &slab->flags);
>  }
>  
>  static inline void slab_clear_node_partial(struct slab *slab)
>  {
> -	clear_bit(PG_workingset, folio_flags(slab_folio(slab), 0));
> +	clear_bit(SL_partial, &slab->flags);
>  }
>  
>  /*
> -- 
> 2.47.2
> 
>