Re: [PATCH 2/3] memcg: unify slab and other kmem pages charging

[Johannes Weiner]

Hi Vladimir,

I'm late, but fwiw these patches are great simplifications. Thanks!

One nit below:

On Mon, Oct 05, 2015 at 01:21:42AM +0300, Vladimir Davydov wrote:
> @@ -2404,36 +2376,59 @@ void __memcg_kmem_put_cache(struct kmem_cache *cachep)
>  		css_put(&cachep->memcg_params.memcg->css);
>  }
>  
> -int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
> +/*
> + * If @memcg != NULL, charge to @memcg, otherwise charge to the memcg the
> + * current task belongs to.
> + */
> +int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order,
> +			struct mem_cgroup *memcg)
>  {
> -	struct mem_cgroup *memcg;
> -	int ret;
> -
> -	memcg = get_mem_cgroup_from_mm(current->mm);
> +	struct page_counter *counter;
> +	unsigned int nr_pages = 1 << order;
> +	bool put = false;
> +	int ret = 0;
>  
> -	if (!memcg_kmem_is_active(memcg)) {
> -		css_put(&memcg->css);
> -		return 0;
> +	if (!memcg) {
> +		memcg = get_mem_cgroup_from_mm(current->mm);
> +		put = true;

I think it'd be better to have an outer function than a magic
parameter for the memcg lookup. Could we fold this in there?

---

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 include/linux/memcontrol.h |  7 ++++---
 mm/memcontrol.c            | 36 ++++++++++++++++++------------------
 mm/slab.h                  |  4 ++--
 3 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 47677ac..730a65d 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -756,8 +756,9 @@ static inline bool memcg_kmem_is_active(struct mem_cgroup *memcg)
  * conditions, but because they are pretty simple, they are expected to be
  * fast.
  */
-int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order,
-			struct mem_cgroup *memcg);
+int __memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order,
+			      struct mem_cgroup *memcg);
+int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order);
 void __memcg_kmem_uncharge(struct page *page, int order);
 
 /*
@@ -797,7 +798,7 @@ static __always_inline int memcg_kmem_charge(struct page *page,
 {
 	if (__memcg_kmem_bypass(gfp))
 		return 0;
-	return __memcg_kmem_charge(page, gfp, order, NULL);
+	return __memcg_kmem_charge(page, gfp, order);
 }
 
 /**
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 15db655..6fc9959 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2378,39 +2378,39 @@ void __memcg_kmem_put_cache(struct kmem_cache *cachep)
 		css_put(&cachep->memcg_params.memcg->css);
 }
 
-/*
- * If @memcg != NULL, charge to @memcg, otherwise charge to the memcg the
- * current task belongs to.
- */
-int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order,
-			struct mem_cgroup *memcg)
+int __memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order,
+			      struct mem_cgroup *memcg)
 {
-	struct page_counter *counter;
 	unsigned int nr_pages = 1 << order;
-	bool put = false;
+	struct page_counter *counter;
 	int ret = 0;
 
-	if (!memcg) {
-		memcg = get_mem_cgroup_from_mm(current->mm);
-		put = true;
-	}
 	if (!memcg_kmem_is_active(memcg))
-		goto out;
+		return 0;
 
 	ret = page_counter_try_charge(&memcg->kmem, nr_pages, &counter);
 	if (ret)
-		goto out;
+		return ret;
 
 	ret = try_charge(memcg, gfp, nr_pages);
 	if (ret) {
 		page_counter_uncharge(&memcg->kmem, nr_pages);
-		goto out;
+		return ret;
 	}
 
 	page->mem_cgroup = memcg;
-out:
-	if (put)
-		css_put(&memcg->css);
+
+	return 0;
+}
+
+int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
+{
+	struct mem_cgroup *memcg;
+	int ret;
+
+	memcg = get_mem_cgroup_from_mm(current->mm);
+	ret = __memcg_kmem_charge_memcg(page, gfp, order, memcg);
+	css_put(&memcg->css);
 	return ret;
 }
 
diff --git a/mm/slab.h b/mm/slab.h
index 3d667a4..27492eb 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -244,8 +244,8 @@ static __always_inline int memcg_charge_slab(struct page *page,
 		return 0;
 	if (is_root_cache(s))
 		return 0;
-	return __memcg_kmem_charge(page, gfp, order,
-				   s->memcg_params.memcg);
+	return __memcg_kmem_charge_memcg(page, gfp, order,
+					 s->memcg_params.memcg);
 }
 
 extern void slab_init_memcg_params(struct kmem_cache *);
-- 
2.6.1
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