On Mon, 21 Feb 2022, Hyeonggon Yoo wrote:
> SLUB sets number of minimum partial slabs for node (min_partial) using
> set_min_partial(). SLUB holds at least min_partial slabs even if they're empty
> to avoid excessive use of page allocator.
>
> set_min_partial() limits value of min_partial between MIN_PARTIAL and
> MAX_PARTIAL. As set_min_partial() can be called by min_partial_store()
> too, Only limit value of min_partial in kmem_cache_open() so that it
> can be changed to value that a user wants.
>
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
I think this makes sense and there is no reason to limit the bounds that
may be set at runtime with undocumented behavior.
However, since set_min_partial() is only setting the value in the
kmem_cache, could we remove the helper function entirely and fold it into
its two callers?
> ---
> mm/slub.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 3a4458976ab7..a4964deccb61 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4002,10 +4002,6 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)
>
> static void set_min_partial(struct kmem_cache *s, unsigned long min)
> {
> - if (min < MIN_PARTIAL)
> - min = MIN_PARTIAL;
> - else if (min > MAX_PARTIAL)
> - min = MAX_PARTIAL;
> s->min_partial = min;
> }
>
> @@ -4184,6 +4180,8 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
>
> static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
> {
> + int min_partial;
> +
> s->flags = kmem_cache_flags(s->size, flags, s->name);
> #ifdef CONFIG_SLAB_FREELIST_HARDENED
> s->random = get_random_long();
> @@ -4215,7 +4213,10 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
> * The larger the object size is, the more slabs we want on the partial
> * list to avoid pounding the page allocator excessively.
> */
> - set_min_partial(s, ilog2(s->size) / 2);
> + min_partial = min(MAX_PARTIAL, ilog2(s->size) / 2);
> + min_partial = max(MIN_PARTIAL, min_partial);
> +
> + set_min_partial(s, min_partial);
>
> set_cpu_partial(s);
>
> --
> 2.33.1
>
>
