mm: memcontrol: introduce obj_cgroup_{un}charge_pages

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 latter 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.

Link: https://lkml.kernel.org/r/20210319163821.20704-3-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index cf7a10d..0f77608 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2874,6 +2874,20 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
        page->memcg_data = (unsigned long)memcg;
 }
 
+static struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg)
+{
+       struct mem_cgroup *memcg;
+
+       rcu_read_lock();
+retry:
+       memcg = obj_cgroup_memcg(objcg);
+       if (unlikely(!css_tryget(&memcg->css)))
+               goto retry;
+       rcu_read_unlock();
+
+       return memcg;
+}
+
 #ifdef CONFIG_MEMCG_KMEM
 int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
                                 gfp_t gfp, bool new_page)
@@ -3025,6 +3039,29 @@ static void memcg_free_cache_id(int id)
        ida_simple_remove(&memcg_cache_ida, id);
 }
 
+static void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg,
+                                     unsigned int nr_pages)
+{
+       struct mem_cgroup *memcg;
+
+       memcg = get_mem_cgroup_from_objcg(objcg);
+       __memcg_kmem_uncharge(memcg, nr_pages);
+       css_put(&memcg->css);
+}
+
+static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
+                                  unsigned int nr_pages)
+{
+       struct mem_cgroup *memcg;
+       int ret;
+
+       memcg = get_mem_cgroup_from_objcg(objcg);
+       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
@@ -3149,19 +3186,8 @@ 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) {
-                       struct mem_cgroup *memcg;
-
-                       rcu_read_lock();
-retry:
-                       memcg = obj_cgroup_memcg(old);
-                       if (unlikely(!css_tryget(&memcg->css)))
-                               goto retry;
-                       rcu_read_unlock();
-
-                       __memcg_kmem_uncharge(memcg, nr_pages);
-                       css_put(&memcg->css);
-               }
+               if (nr_pages)
+                       obj_cgroup_uncharge_pages(old, nr_pages);
 
                /*
                 * The leftover is flushed to the centralized per-memcg value.
@@ -3219,7 +3245,6 @@ 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;
 
@@ -3236,24 +3261,16 @@ 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;
 }