[PATCH -mm] memcg: zap memcg_can_account_kmem

[PATCH -mm] memcg: zap memcg_can_account_kmem

[Vladimir Davydov]

memcg_can_account_kmem() returns true iff

    !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
                                   memcg_kmem_is_active(memcg);

To begin with the !mem_cgroup_is_root(memcg) check is useless, because
one can't enable kmem accounting for the root cgroup (mem_cgroup_write()
returns EINVAL on an attempt to set the limit on the root cgroup).

Furthermore, the !mem_cgroup_disabled() check also seems to be
redundant. The point is memcg_can_account_kmem() is called from three
places: mem_cgroup_salbinfo_read(), __memcg_kmem_get_cache(), and
__memcg_kmem_newpage_charge(). The latter two functions are only invoked
if memcg_kmem_enabled() returns true, which implies that the memory
cgroup subsystem is enabled. And mem_cgroup_slabinfo_read() shows the
output of memory.kmem.slabinfo, which won't exist if the memory cgroup
is completely disabled.

So let's substitute all the calls to memcg_can_account_kmem() with plain
memcg_kmem_is_active(), and kill the former.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
---
 mm/memcontrol.c |   12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1ec22bf380d0..63d58d79470d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2786,12 +2786,6 @@ static DEFINE_MUTEX(memcg_slab_mutex);
 
 static DEFINE_MUTEX(activate_kmem_mutex);
 
-static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
-{
-	return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
-		memcg_kmem_is_active(memcg);
-}
-
 /*
  * This is a bit cumbersome, but it is rarely used and avoids a backpointer
  * in the memcg_cache_params struct.
@@ -2811,7 +2805,7 @@ static int mem_cgroup_slabinfo_read(struct seq_file *m, void *v)
 	struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
 	struct memcg_cache_params *params;
 
-	if (!memcg_can_account_kmem(memcg))
+	if (!memcg_kmem_is_active(memcg))
 		return -EIO;
 
 	print_slabinfo_header(m);
@@ -3188,7 +3182,7 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep,
 	rcu_read_lock();
 	memcg = mem_cgroup_from_task(rcu_dereference(current->mm->owner));
 
-	if (!memcg_can_account_kmem(memcg))
+	if (!memcg_kmem_is_active(memcg))
 		goto out;
 
 	memcg_cachep = cache_from_memcg_idx(cachep, memcg_cache_id(memcg));
@@ -3273,7 +3267,7 @@ __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
 
 	memcg = get_mem_cgroup_from_mm(current->mm);
 
-	if (!memcg_can_account_kmem(memcg)) {
+	if (!memcg_kmem_is_active(memcg)) {
 		css_put(&memcg->css);
 		return true;
 	}
-- 
1.7.10.4

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Re: [PATCH -mm] memcg: zap memcg_can_account_kmem

[Johannes Weiner]

On Wed, Sep 24, 2014 at 06:52:41PM +0400, Vladimir Davydov wrote:
> memcg_can_account_kmem() returns true iff
> 
>     !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
>                                    memcg_kmem_is_active(memcg);
> 
> To begin with the !mem_cgroup_is_root(memcg) check is useless, because
> one can't enable kmem accounting for the root cgroup (mem_cgroup_write()
> returns EINVAL on an attempt to set the limit on the root cgroup).
> 
> Furthermore, the !mem_cgroup_disabled() check also seems to be
> redundant. The point is memcg_can_account_kmem() is called from three
> places: mem_cgroup_salbinfo_read(), __memcg_kmem_get_cache(), and
> __memcg_kmem_newpage_charge(). The latter two functions are only invoked
> if memcg_kmem_enabled() returns true, which implies that the memory
> cgroup subsystem is enabled. And mem_cgroup_slabinfo_read() shows the
> output of memory.kmem.slabinfo, which won't exist if the memory cgroup
> is completely disabled.
> 
> So let's substitute all the calls to memcg_can_account_kmem() with plain
> memcg_kmem_is_active(), and kill the former.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>

Yes, the two checks look indeed redundant.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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