[PATCH 6/7] mm: memcg/slab: cache page number in memcg_(un)charge_slab()

[Roman Gushchin]

There are many places in memcg_charge_slab() and memcg_uncharge_slab()
which are calculating the number of pages to charge, css references to
grab etc depending on the order of the slab page.

Let's simplify the code by calculating it once and caching in the
local variable.

Signed-off-by: Roman Gushchin <guro@xxxxxx>
---
 mm/slab.h | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/mm/slab.h b/mm/slab.h
index d96c87a30a9b..43f8ce4aa325 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -348,6 +348,7 @@ static __always_inline int memcg_charge_slab(struct page *page,
 					     gfp_t gfp, int order,
 					     struct kmem_cache *s)
 {
+	unsigned int nr_pages = 1 << order;
 	struct mem_cgroup *memcg;
 	struct lruvec *lruvec;
 	int ret;
@@ -360,21 +361,21 @@ static __always_inline int memcg_charge_slab(struct page *page,
 
 	if (unlikely(!memcg || mem_cgroup_is_root(memcg))) {
 		mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
-				    (1 << order));
-		percpu_ref_get_many(&s->memcg_params.refcnt, 1 << order);
+				    nr_pages);
+		percpu_ref_get_many(&s->memcg_params.refcnt, nr_pages);
 		return 0;
 	}
 
-	ret = memcg_kmem_charge_memcg(memcg, gfp, 1 << order);
+	ret = memcg_kmem_charge_memcg(memcg, gfp, nr_pages);
 	if (ret)
 		goto out;
 
 	lruvec = mem_cgroup_lruvec(memcg, page_pgdat(page));
-	mod_lruvec_state(lruvec, cache_vmstat_idx(s), 1 << order);
+	mod_lruvec_state(lruvec, cache_vmstat_idx(s), nr_pages);
 
 	/* transer try_charge() page references to kmem_cache */
-	percpu_ref_get_many(&s->memcg_params.refcnt, 1 << order);
-	css_put_many(&memcg->css, 1 << order);
+	percpu_ref_get_many(&s->memcg_params.refcnt, nr_pages);
+	css_put_many(&memcg->css, nr_pages);
 out:
 	css_put(&memcg->css);
 	return ret;
@@ -387,6 +388,7 @@ static __always_inline int memcg_charge_slab(struct page *page,
 static __always_inline void memcg_uncharge_slab(struct page *page, int order,
 						struct kmem_cache *s)
 {
+	unsigned int nr_pages = 1 << order;
 	struct mem_cgroup *memcg;
 	struct lruvec *lruvec;
 
@@ -394,15 +396,15 @@ static __always_inline void memcg_uncharge_slab(struct page *page, int order,
 	memcg = READ_ONCE(s->memcg_params.memcg);
 	if (likely(!mem_cgroup_is_root(memcg))) {
 		lruvec = mem_cgroup_lruvec(memcg, page_pgdat(page));
-		mod_lruvec_state(lruvec, cache_vmstat_idx(s), -(1 << order));
-		memcg_kmem_uncharge_memcg(memcg, order);
+		mod_lruvec_state(lruvec, cache_vmstat_idx(s), -nr_pages);
+		memcg_kmem_uncharge_memcg(memcg, nr_pages);
 	} else {
 		mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
-				    -(1 << order));
+				    -nr_pages);
 	}
 	rcu_read_unlock();
 
-	percpu_ref_put_many(&s->memcg_params.refcnt, 1 << order);
+	percpu_ref_put_many(&s->memcg_params.refcnt, nr_pages);
 }
 
 extern void slab_init_memcg_params(struct kmem_cache *);
-- 
2.21.1