On Tue, Jan 04, 2022 at 01:10:43AM +0100, Vlastimil Babka wrote:
> The fields 'next' and 'slabs' are only used when CONFIG_SLUB_CPU_PARTIAL
> is enabled. We can put their definition to #ifdef to prevent accidental
> use when disabled.
>
> Currenlty show_slab_objects() and slabs_cpu_partial_show() contain code
> accessing the slabs field that's effectively dead with
> CONFIG_SLUB_CPU_PARTIAL=n through the wrappers slub_percpu_partial() and
> slub_percpu_partial_read_once(), but to prevent a compile error, we need
> to hide all this code behind #ifdef.
>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> Reviewed-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> Tested-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> ---
> mm/slab.h | 2 ++
> mm/slub.c | 8 ++++++--
> 2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/mm/slab.h b/mm/slab.h
> index 362832f465e6..ac8be7dab535 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -25,10 +25,12 @@ struct slab {
> union {
> struct list_head slab_list;
> struct rcu_head rcu_head;
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
> struct {
> struct slab *next;
> int slabs; /* Nr of slabs left */
> };
> +#endif
> };
> struct kmem_cache *slab_cache;
> /* Double-word boundary */
> diff --git a/mm/slub.c b/mm/slub.c
> index d08ba1025aae..261474092e43 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5258,6 +5258,7 @@ static ssize_t show_slab_objects(struct kmem_cache *s,
> total += x;
> nodes[node] += x;
>
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
> slab = slub_percpu_partial_read_once(c);
> if (slab) {
> node = slab_nid(slab);
> @@ -5270,6 +5271,7 @@ static ssize_t show_slab_objects(struct kmem_cache *s,
> total += x;
> nodes[node] += x;
> }
> +#endif
> }
> }
>
> @@ -5469,9 +5471,10 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
> {
> int objects = 0;
> int slabs = 0;
> - int cpu;
> + int cpu __maybe_unused;
> int len = 0;
>
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
> for_each_online_cpu(cpu) {
> struct slab *slab;
>
> @@ -5480,12 +5483,13 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
> if (slab)
> slabs += slab->slabs;
> }
> +#endif
>
> /* Approximate half-full slabs, see slub_set_cpu_partial() */
> objects = (slabs * oo_objects(s->oo)) / 2;
> len += sysfs_emit_at(buf, len, "%d(%d)", objects, slabs);
>
> -#ifdef CONFIG_SMP
> +#if defined(CONFIG_SLUB_CPU_PARTIAL) && defined(CONFIG_SMP)
CONFIG_SLUB_CPU_PARTIAL is defined like:
config SLUB_CPU_PARTIAL
default y
depends on SLUB && SMP
So I guess the " && defined(CONFIG_SMP)" part can be dropped.
Otherwise lgtm.
Reviewed-by: Roman Gushchin <guro@xxxxxx>
