Sometimes we need to get a memcg pointer from a charged kernel object.
The right way to get it depends on whether it's a proper slab object
or it's backed by raw pages (e.g. it's a vmalloc alloction). In the
first case the kmem_cache->memcg_params.memcg indirection should be
used; in other cases it's just page->mem_cgroup.
To simplify this task and hide the implementation details let's
introduce a mem_cgroup_from_obj() helper, which takes a pointer
to any kernel object and returns a valid memcg pointer or NULL.
Passing a kernel address rather than a pointer to a page will allow
to use this helper for per-object (rather than per-page) tracked
objects in the future.
The caller is still responsible to ensure that the returned memcg
isn't going away underneath: take the rcu read lock, cgroup mutex etc;
depending on the context.
mem_cgroup_from_kmem() defined in mm/list_lru.c is now obsolete
and can be removed.
Signed-off-by: Roman Gushchin <guro@xxxxxx>
---
include/linux/memcontrol.h | 7 +++++++
mm/list_lru.c | 12 +-----------
mm/memcontrol.c | 32 +++++++++++++++++++++++++++++---
3 files changed, 37 insertions(+), 14 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index c372bed6be80..24c50d004c46 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1427,6 +1427,8 @@ 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);
+
#else
static inline int memcg_kmem_charge_page(struct page *page, gfp_t gfp,
@@ -1470,6 +1472,11 @@ 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 */
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 0f1f6b06b7f3..8de5e3784ee4 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -57,16 +57,6 @@ list_lru_from_memcg_idx(struct list_lru_node *nlru, int idx)
return &nlru->lru;
}
-static __always_inline struct mem_cgroup *mem_cgroup_from_kmem(void *ptr)
-{
- struct page *page;
-
- if (!memcg_kmem_enabled())
- return NULL;
- page = virt_to_head_page(ptr);
- return memcg_from_slab_page(page);
-}
-
static inline struct list_lru_one *
list_lru_from_kmem(struct list_lru_node *nlru, void *ptr,
struct mem_cgroup **memcg_ptr)
@@ -77,7 +67,7 @@ list_lru_from_kmem(struct list_lru_node *nlru, void *ptr,
if (!nlru->memcg_lrus)
goto out;
- memcg = mem_cgroup_from_kmem(ptr);
+ memcg = mem_cgroup_from_obj(ptr);
if (!memcg)
goto out;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8798702d165b..43010471621c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -757,13 +757,12 @@ void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val)
{
- struct page *page = virt_to_head_page(p);
- pg_data_t *pgdat = page_pgdat(page);
+ pg_data_t *pgdat = page_pgdat(virt_to_page(p));
struct mem_cgroup *memcg;
struct lruvec *lruvec;
rcu_read_lock();
- memcg = memcg_from_slab_page(page);
+ memcg = mem_cgroup_from_obj(p);
/* Untracked pages have no memcg, no lruvec. Update only the node */
if (!memcg || memcg == root_mem_cgroup) {
@@ -2636,6 +2635,33 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
}
#ifdef CONFIG_MEMCG_KMEM
+/*
+ * 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;
--
2.24.1
