On Thu, Nov 26, 2020 at 09:55:24PM -0800, Shakeel Butt wrote:

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.

Ok, I agree. Here is an updated version.

Thank you for looking in!

--

From 456ce03f1c91baf5e2441dce0649e09617437fe4 Mon Sep 17 00:00:00 2001

From: Roman Gushchin guro@fb.com Date: Thu, 26 Nov 2020 07:39:57 -0800 Subject: [PATCH v2] mm: memcg/slab: fix obj_cgroup_charge() return value handling

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..0698a3c0a9da 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 false if the allocation should fail. + */ +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 true; + + if (!(flags & __GFP_ACCOUNT) && !(s->flags & SLAB_ACCOUNT)) + return true; + objcg = get_obj_cgroup_from_current(); if (!objcg) - return NULL; + return true;

if (obj_cgroup_charge(objcg, flags, objects * obj_full_size(s))) { obj_cgroup_put(objcg); - return NULL; + return false; }

- return objcg; + *objcgp = objcg; + return true; }

static inline void mod_objcg_state(struct obj_cgroup *objcg, @@ -298,7 +308,7 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s, unsigned long off; size_t i;

- if (!objcg) + if (!memcg_kmem_enabled() || !objcg) return;

flags &= ~__GFP_ACCOUNT; @@ -382,11 +392,11 @@ static inline void memcg_free_page_obj_cgroups(struct page *page) { }

-static inline struct obj_cgroup *memcg_slab_pre_alloc_hook(struct kmem_cache *s, - size_t objects, - gfp_t flags) +static inline bool memcg_slab_pre_alloc_hook(struct kmem_cache *s, + struct obj_cgroup **objcgp, + size_t objects, gfp_t flags) { - return NULL; + return true; }

static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s, @@ -494,9 +504,8 @@ static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s, if (should_failslab(s, flags)) return NULL;

- if (memcg_kmem_enabled() && - ((flags & __GFP_ACCOUNT) || (s->flags & SLAB_ACCOUNT))) - *objcgp = memcg_slab_pre_alloc_hook(s, size, flags); + if (!memcg_slab_pre_alloc_hook(s, objcgp, size, flags)) + return NULL;

return s; } @@ -515,8 +524,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s, s->flags, flags); }

- if (memcg_kmem_enabled()) - memcg_slab_post_alloc_hook(s, objcg, flags, size, p); + memcg_slab_post_alloc_hook(s, objcg, flags, size, p); }

#ifndef CONFIG_SLOB