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SubjectRe: [PATCH v3 09/19] mm: memcg/slab: charge individual slab objects instead of pages
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On 4/22/20 10:46 PM, Roman Gushchin wrote:
> Switch to per-object accounting of non-root slab objects.
>
> Charging is performed using obj_cgroup API in the pre_alloc hook.
> Obj_cgroup is charged with the size of the object and the size
> of metadata: as now it's the size of an obj_cgroup pointer.
> If the amount of memory has been charged successfully, the actual
> allocation code is executed. Otherwise, -ENOMEM is returned.
>
> In the post_alloc hook if the actual allocation succeeded,
> corresponding vmstats are bumped and the obj_cgroup pointer is saved.
> Otherwise, the charge is canceled.
>
> On the free path obj_cgroup pointer is obtained and used to uncharge
> the size of the releasing object.
>
> Memcg and lruvec counters are now representing only memory used
> by active slab objects and do not include the free space. The free
> space is shared and doesn't belong to any specific cgroup.
>
> Global per-node slab vmstats are still modified from (un)charge_slab_page()
> functions. The idea is to keep all slab pages accounted as slab pages
> on system level.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>

Suggestion below:

> @@ -568,32 +548,33 @@ static __always_inline int charge_slab_page(struct page *page,
> gfp_t gfp, int order,
> struct kmem_cache *s)
> {
> - int ret;
> -
> - if (is_root_cache(s)) {
> - mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
> - PAGE_SIZE << order);
> - return 0;
> - }
> +#ifdef CONFIG_MEMCG_KMEM
> + if (!is_root_cache(s)) {

This could also benefit from memcg_kmem_enabled() static key test AFAICS. Maybe
even have a wrapper for both tests together?

> + int ret;
>
> - ret = memcg_alloc_page_obj_cgroups(page, gfp, objs_per_slab(s));
> - if (ret)
> - return ret;
> + ret = memcg_alloc_page_obj_cgroups(page, gfp, objs_per_slab(s));

You created memcg_alloc_page_obj_cgroups() empty variant for !CONFIG_MEMCG_KMEM
but now the only caller is under CONFIG_MEMCG_KMEM.

> + if (ret)
> + return ret;
>
> - return memcg_charge_slab(page, gfp, order, s);
> + percpu_ref_get_many(&s->memcg_params.refcnt, 1 << order);

Perhaps moving this refcount into memcg_alloc_page_obj_cgroups() (maybe the name
should be different then) will allow you to not add #ifdef CONFIG_MEMCG_KMEM in
this function.

Maybe this is all moot after patch 12/19, will find out :)

> + }
> +#endif
> + mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
> + PAGE_SIZE << order);
> + return 0;
> }
>
> static __always_inline void uncharge_slab_page(struct page *page, int order,
> struct kmem_cache *s)
> {
> - if (is_root_cache(s)) {
> - mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
> - -(PAGE_SIZE << order));
> - return;
> +#ifdef CONFIG_MEMCG_KMEM
> + if (!is_root_cache(s)) {

Everything from above also applies here.

> + memcg_free_page_obj_cgroups(page);
> + percpu_ref_put_many(&s->memcg_params.refcnt, 1 << order);
> }
> -
> - memcg_free_page_obj_cgroups(page);
> - memcg_uncharge_slab(page, order, s);
> +#endif
> + mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
> + -(PAGE_SIZE << order));
> }
>
> static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)


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