On 4/22/20 10:46 PM, Roman Gushchin wrote:
> Allocate and release memory to store obj_cgroup pointers for each
> non-root slab page. Reuse page->mem_cgroup pointer to store a pointer
> to the allocated space.
>
> To distinguish between obj_cgroups and memcg pointers in case
> when it's not obvious which one is used (as in page_cgroup_ino()),
> let's always set the lowest bit in the obj_cgroup case.
>
> Signed-off-by: Roman Gushchin <guro@xxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
But I have a suggestion:
...
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -191,4 +191,6 @@ static inline unsigned int obj_to_index(const struct kmem_cache *cache,
> cache->reciprocal_size);
> }
>
> +extern int objs_per_slab(struct kmem_cache *cache);
> +
> #endif /* _LINUX_SLUB_DEF_H */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 7f87a0eeafec..63826e460b3f 100644
...
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5992,4 +5992,9 @@ ssize_t slabinfo_write(struct file *file, const char __user *buffer,
> {
> return -EIO;
> }
> +
> +int objs_per_slab(struct kmem_cache *cache)
> +{
> + return oo_objects(cache->oo);
> +}
> #endif /* CONFIG_SLUB_DEBUG */
>
It's somewhat unfortunate to function call just for this. Although perhaps
compiler can be smart enough as charge_slab_page() (that callse objs_per_slab())
is inline and called from alloc_slab_page() which is also in mm/slub.c.
But it might be also a bit wasteful in case SLUB doesn't manage to allocate its
desired order, but smaller. The actual number of objects is then in page->objects.
So ideally this should use something like objs_per_slab_page(cache, page) where
SLAB supplies cache->num and SLUB page->objects, both implementations inline,
and ignoring the other parameter?
