Re: [PATCH 3/3] memcg: simplify and inline __mem_cgroup_from_kmem

[Vladimir Davydov <vdavydov@virtuozzo.com>]

On Fri, Oct 16, 2015 at 03:12:23PM -0700, Hugh Dickins wrote:
...
> Are you expecting to use mem_cgroup_from_kmem() from other places
> in future?  Seems possible; but at present it's called from only

Not in the near future. At least, currently I can't think of any other
use for it except list_lru_from_kmem.

> one place, and (given how memcontrol.h has somehow managed to avoid
> including mm.h all these years), I thought it would be nice to avoid
> it for just this; and fixed my build with the patch below last night.
> Whatever you all think best: just wanted to point out an alternative.

Makes sense, thanks!

I would even inline mem_cgroup_from_kmem to list_lru_from_kmem:

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 47677acb4516..2077b9bb4883 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -831,16 +831,6 @@ static __always_inline void memcg_kmem_put_cache(struct kmem_cache *cachep)
 	if (memcg_kmem_enabled())
 		__memcg_kmem_put_cache(cachep);
 }
-
-static __always_inline struct mem_cgroup *mem_cgroup_from_kmem(void *ptr)
-{
-	struct page *page;
-
-	if (!memcg_kmem_enabled())
-		return NULL;
-	page = virt_to_head_page(ptr);
-	return page->mem_cgroup;
-}
 #else
 #define for_each_memcg_cache_index(_idx)	\
 	for (; NULL; )
@@ -886,11 +876,6 @@ memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp)
 static inline void memcg_kmem_put_cache(struct kmem_cache *cachep)
 {
 }
-
-static inline struct mem_cgroup *mem_cgroup_from_kmem(void *ptr)
-{
-	return NULL;
-}
 #endif /* CONFIG_MEMCG_KMEM */
 #endif /* _LINUX_MEMCONTROL_H */
 
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 28237476b055..00d0a70af70a 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -68,10 +68,10 @@ list_lru_from_kmem(struct list_lru_node *nlru, void *ptr)
 {
 	struct mem_cgroup *memcg;
 
-	if (!nlru->memcg_lrus)
+	if (!memcg_kmem_enabled() || !nlru->memcg_lrus)
 		return &nlru->lru;
 
-	memcg = mem_cgroup_from_kmem(ptr);
+	memcg = virt_to_head_page(ptr)->mem_cgroup;
 	if (!memcg)
 		return &nlru->lru;
 

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