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Subject[PATCH] Re: [PATCH v3 1/2] mm: memcg: remote memcg charging for kmem allocations
Date
On Thu, Mar 15, 2018 at 10:49 AM, Michal Hocko <mhocko@kernel.org> wrote:
> Charging path is still a _hot path_. Especially when the kmem accounting
> is enabled by default. You cannot simply downplay the overhead. We have
> _one_ user but all users should pay the price. This is simply hard to
> justify. Maybe we can thing of something that would put the burden on
> the charging context?

What do you think of the following?

Signed-off-by: Shakeel Butt <shakeelb@google.com>
---
mm/memcontrol.c | 37 ++++++++++++++++++-------------------
1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5d3ea8799a2c..205043283716 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -701,6 +701,20 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
return memcg;
}

+static __always_inline struct mem_cgroup *get_mem_cgroup(
+ struct mem_cgroup *memcg, struct mm_struct *mm)
+{
+ if (unlikely(memcg)) {
+ rcu_read_lock();
+ if (css_tryget_online(&memcg->css)) {
+ rcu_read_unlock();
+ return memcg;
+ }
+ rcu_read_unlock();
+ }
+ return get_mem_cgroup_from_mm(mm);
+}
+
/**
* mem_cgroup_iter - iterate over memory cgroup hierarchy
* @root: hierarchy root
@@ -2119,15 +2133,6 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
}

#ifndef CONFIG_SLOB
-static struct mem_cgroup *get_mem_cgroup(struct mem_cgroup *memcg)
-{
- rcu_read_lock();
- if (!css_tryget_online(&memcg->css))
- memcg = NULL;
- rcu_read_unlock();
- return memcg;
-}
-
static int memcg_alloc_cache_id(void)
{
int id, size;
@@ -2257,7 +2262,7 @@ static inline bool memcg_kmem_bypass(void)
*/
struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep)
{
- struct mem_cgroup *memcg = NULL;
+ struct mem_cgroup *memcg;
struct kmem_cache *memcg_cachep;
int kmemcg_id;

@@ -2269,10 +2274,7 @@ struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep)
if (current->memcg_kmem_skip_account)
return cachep;

- if (current->target_memcg)
- memcg = get_mem_cgroup(current->target_memcg);
- if (!memcg)
- memcg = get_mem_cgroup_from_mm(current->mm);
+ memcg = get_mem_cgroup(current->target_memcg, current->mm);
kmemcg_id = READ_ONCE(memcg->kmemcg_id);
if (kmemcg_id < 0)
goto out;
@@ -2350,16 +2352,13 @@ int memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order,
*/
int memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
{
- struct mem_cgroup *memcg = NULL;
+ struct mem_cgroup *memcg;
int ret = 0;

if (memcg_kmem_bypass())
return 0;

- if (current->target_memcg)
- memcg = get_mem_cgroup(current->target_memcg);
- if (!memcg)
- memcg = get_mem_cgroup_from_mm(current->mm);
+ memcg = get_mem_cgroup(current->target_memcg, current->mm);
if (!mem_cgroup_is_root(memcg)) {
ret = memcg_kmem_charge_memcg(page, gfp, order, memcg);
if (!ret)
--
2.17.0.484.g0c8726318c-goog
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