[PATCH v4 1/5] mm: memcontrol: introduce obj_cgroup_{un}charge_pages

From: Muchun Song <hidden>
Date: 2021-03-18 11:09:09
Also in: lkml
Subsystem: control group - memory resource controller (memcg), memory management, the rest · Maintainers: Johannes Weiner, Michal Hocko, Roman Gushchin, Shakeel Butt, Andrew Morton, Linus Torvalds

We know that the unit of slab object charging is bytes, the unit of
kmem page charging is PAGE_SIZE. If we want to reuse obj_cgroup APIs
to charge the kmem pages, we should pass PAGE_SIZE (as third parameter)
to obj_cgroup_charge(). Because the size is already PAGE_SIZE, we can
skip touch the objcg stock. And obj_cgroup_{un}charge_pages() are
introduced to charge in units of page level.

In the later patch, we also can reuse those two helpers to charge or
uncharge a number of kernel pages to a object cgroup. This is just
a code movement without any functional changes.

Signed-off-by: Muchun Song <redacted>
Acked-by: Roman Gushchin <redacted>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <redacted>
---
 mm/memcontrol.c | 46 +++++++++++++++++++++++++++++++---------------
 1 file changed, 31 insertions(+), 15 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 845eec01ef9d..fc22da9805fb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -3056,6 +3056,34 @@ static void memcg_free_cache_id(int id)
 	ida_simple_remove(&memcg_cache_ida, id);
 }
 
+static inline void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg,
+					     unsigned int nr_pages)
+{
+	rcu_read_lock();
+	__memcg_kmem_uncharge(obj_cgroup_memcg(objcg), nr_pages);
+	rcu_read_unlock();
+}
+
+static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
+				   unsigned int nr_pages)
+{
+	struct mem_cgroup *memcg;
+	int ret;
+
+	rcu_read_lock();
+retry:
+	memcg = obj_cgroup_memcg(objcg);
+	if (unlikely(!css_tryget(&memcg->css)))
+		goto retry;
+	rcu_read_unlock();
+
+	ret = __memcg_kmem_charge(memcg, gfp, nr_pages);
+
+	css_put(&memcg->css);
+
+	return ret;
+}
+
 /**
  * __memcg_kmem_charge: charge a number of kernel pages to a memcg
  * @memcg: memory cgroup to charge

@@ -3180,11 +3208,8 @@ static void drain_obj_stock(struct memcg_stock_pcp *stock)
 		unsigned int nr_pages = stock->nr_bytes >> PAGE_SHIFT;
 		unsigned int nr_bytes = stock->nr_bytes & (PAGE_SIZE - 1);
 
-		if (nr_pages) {
-			rcu_read_lock();
-			__memcg_kmem_uncharge(obj_cgroup_memcg(old), nr_pages);
-			rcu_read_unlock();
-		}
+		if (nr_pages)
+			obj_cgroup_uncharge_pages(old, nr_pages);
 
 		/*
 		 * The leftover is flushed to the centralized per-memcg value.

@@ -3242,7 +3267,6 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
 
 int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size)
 {
-	struct mem_cgroup *memcg;
 	unsigned int nr_pages, nr_bytes;
 	int ret;

@@ -3259,24 +3283,16 @@ int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size)
 	 * refill_obj_stock(), called from this function or
 	 * independently later.
 	 */
-	rcu_read_lock();
-retry:
-	memcg = obj_cgroup_memcg(objcg);
-	if (unlikely(!css_tryget(&memcg->css)))
-		goto retry;
-	rcu_read_unlock();
-
 	nr_pages = size >> PAGE_SHIFT;
 	nr_bytes = size & (PAGE_SIZE - 1);
 
 	if (nr_bytes)
 		nr_pages += 1;
 
-	ret = __memcg_kmem_charge(memcg, gfp, nr_pages);
+	ret = obj_cgroup_charge_pages(objcg, gfp, nr_pages);
 	if (!ret && nr_bytes)
 		refill_obj_stock(objcg, PAGE_SIZE - nr_bytes);
 
-	css_put(&memcg->css);
 	return ret;
 }

-- 
2.11.0

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