Re: [PATCH] mm: memcg/slab: fix obj_cgroup_charge() return value handling

On Thu, Nov 26, 2020 at 8:14 PM Roman Gushchin guro@fb.com wrote:

Commit 10befea91b61 ("mm: memcg/slab: use a single set of kmem_caches for all allocations") introduced a regression into the handling of the obj_cgroup_charge() return value. If a non-zero value is returned (indicating of exceeding one of memory.max limits), the allocation should fail, instead of falling back to non-accounted mode.

To make the code more readable, move memcg_slab_pre_alloc_hook() and memcg_slab_post_alloc_hook() calling conditions into bodies of these hooks.

Fixes: 10befea91b61 ("mm: memcg/slab: use a single set of kmem_caches for all allocations") Signed-off-by: Roman Gushchin guro@fb.com Cc: stable@vger.kernel.org

---

mm/slab.h | 40 ++++++++++++++++++++++++---------------- 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/mm/slab.h b/mm/slab.h index 59aeb0d9f11b..5dc89d8fb05e 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -257,22 +257,32 @@ static inline size_t obj_full_size(struct kmem_cache *s) return s->size + sizeof(struct obj_cgroup *); }

-static inline struct obj_cgroup *memcg_slab_pre_alloc_hook(struct kmem_cache *s,

•                                                      size_t objects,
  

•                                                      gfp_t flags)
  

+/*

• • Returns true if the allocation should fail.

IMO returning false if the allocation should fail makes this more clear. Otherwise the patch looks good to me.

• */

+static inline bool memcg_slab_pre_alloc_hook(struct kmem_cache *s,

•                                        struct obj_cgroup **objcgp,
  

•                                        size_t objects, gfp_t flags)
  

{ struct obj_cgroup *objcg;

•   if (!memcg_kmem_enabled())
  

•           return false;
  

•   if (!(flags & __GFP_ACCOUNT) && !(s->flags & SLAB_ACCOUNT))
  

•           return false;
  

•   objcg = get_obj_cgroup_from_current();
    if (!objcg)
  

•           return NULL;
  

•           return false;
  
    if (obj_cgroup_charge(objcg, flags, objects * obj_full_size(s))) {
            obj_cgroup_put(objcg);
  

•           return NULL;
  

•           return true;
    }
  
  

•   return objcg;
  

•   *objcgp = objcg;
  

•   return false;
  

}