Commit 8380ce47 authored by Roman Gushchin's avatar Roman Gushchin Committed by Linus Torvalds
Browse files

mm: fork: fix kernel_stack memcg stats for various stack implementations

Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio the
space for task stacks can be allocated using __vmalloc_node_range(),
alloc_pages_node() and kmem_cache_alloc_node().

In the first and the second cases page->mem_cgroup pointer is set, but
in the third it's not: memcg membership of a slab page should be
determined using the memcg_from_slab_page() function, which looks at
page->slab_cache->memcg_params.memcg .  In this case, using
mod_memcg_page_state() (as in account_kernel_stack()) is incorrect:
page->mem_cgroup pointer is NULL even for pages charged to a non-root
memory cgroup.

It can lead to kernel_stack per-memcg counters permanently showing 0 on
some architectures (depending on the configuration).

In order to fix it, let's introduce a mod_memcg_obj_state() helper,
which takes a pointer to a kernel object as a first argument, uses
mem_cgroup_from_obj() to get a RCU-protected memcg pointer and calls
mod_memcg_state().  It allows to handle all possible configurations
(CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE values) without
spilling any memcg/kmem specifics into fork.c .

Note: This is a special version of the patch created for stable
backports.  It contains code from the following two patches:
  - mm: memcg/slab: introduce mem_cgroup_from_obj()
  - mm: fork: fix kernel_stack memcg stats for various stack implementations

[ introduce mem_cgroup_from_obj()]
Fixes: 4d96ba35

 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
Signed-off-by: default avatarRoman Gushchin <>
Signed-off-by: default avatarAndrew Morton <>
Reviewed-by: default avatarShakeel Butt <>
Acked-by: default avatarJohannes Weiner <>
Cc: Michal Hocko <>
Cc: Bharata B Rao <>
Cc: Shakeel Butt <>
Cc: <>

Signed-off-by: default avatarLinus Torvalds <>
parent 726b7bbe
......@@ -695,6 +695,7 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
int val);
void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val);
void mod_memcg_obj_state(void *p, int idx, int val);
static inline void mod_lruvec_state(struct lruvec *lruvec,
enum node_stat_item idx, int val)
......@@ -1123,6 +1124,10 @@ static inline void __mod_lruvec_slab_state(void *p, enum node_stat_item idx,
__mod_node_page_state(page_pgdat(page), idx, val);
static inline void mod_memcg_obj_state(void *p, int idx, int val)
static inline
unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
gfp_t gfp_mask,
......@@ -1427,6 +1432,8 @@ static inline int memcg_cache_id(struct mem_cgroup *memcg)
return memcg ? memcg->kmemcg_id : -1;
struct mem_cgroup *mem_cgroup_from_obj(void *p);
static inline int memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
......@@ -1468,6 +1475,11 @@ static inline void memcg_put_cache_ids(void)
static inline struct mem_cgroup *mem_cgroup_from_obj(void *p)
return NULL;
#endif /* CONFIG_MEMCG_KMEM */
#endif /* _LINUX_MEMCONTROL_H */
......@@ -397,8 +397,8 @@ static void account_kernel_stack(struct task_struct *tsk, int account)
mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB,
THREAD_SIZE / 1024 * account);
mod_memcg_page_state(first_page, MEMCG_KERNEL_STACK_KB,
account * (THREAD_SIZE / 1024));
mod_memcg_obj_state(stack, MEMCG_KERNEL_STACK_KB,
account * (THREAD_SIZE / 1024));
......@@ -777,6 +777,17 @@ void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val)
void mod_memcg_obj_state(void *p, int idx, int val)
struct mem_cgroup *memcg;
memcg = mem_cgroup_from_obj(p);
if (memcg)
mod_memcg_state(memcg, idx, val);
* __count_memcg_events - account VM events in a cgroup
* @memcg: the memory cgroup
......@@ -2661,6 +2672,33 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
* Returns a pointer to the memory cgroup to which the kernel object is charged.
* The caller must ensure the memcg lifetime, e.g. by taking rcu_read_lock(),
* cgroup_mutex, etc.
struct mem_cgroup *mem_cgroup_from_obj(void *p)
struct page *page;
if (mem_cgroup_disabled())
return NULL;
page = virt_to_head_page(p);
* Slab pages don't have page->mem_cgroup set because corresponding
* kmem caches can be reparented during the lifetime. That's why
* memcg_from_slab_page() should be used instead.
if (PageSlab(page))
return memcg_from_slab_page(page);
/* All other pages use page->mem_cgroup */
return page->mem_cgroup;
static int memcg_alloc_cache_id(void)
int id, size;
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