Re: [PATCH -mm] memcg: zap memcg_can_account_kmem

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 <redacted>

Yes, the two checks look indeed redundant.

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

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