On 04/03/2013 07:31 PM, Michal Hocko wrote: > On Wed 03-04-13 17:12:21, Li Zefan wrote: >> Use css_get()/css_put() instead of mem_cgroup_get()/mem_cgroup_put(). >> >> Signed-off-by: Li Zefan <[email protected]> >> --- >> mm/memcontrol.c | 10 +++++----- >> 1 file changed, 5 insertions(+), 5 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 43ca91d..dafacb8 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -3191,7 +3191,7 @@ void memcg_release_cache(struct kmem_cache *s) >> list_del(&s->memcg_params->list); >> mutex_unlock(&memcg->slab_caches_mutex); >> >> - mem_cgroup_put(memcg); >> + css_put(&memcg->css); >> out: >> kfree(s->memcg_params); >> } >> @@ -3350,16 +3350,18 @@ static struct kmem_cache >> *memcg_create_kmem_cache(struct mem_cgroup *memcg, >> >> mutex_lock(&memcg_cache_mutex); >> new_cachep = cachep->memcg_params->memcg_caches[idx]; >> - if (new_cachep) >> + if (new_cachep) { >> + css_put(&memcg->css); >> goto out; >> + } >> >> new_cachep = kmem_cache_dup(memcg, cachep); >> if (new_cachep == NULL) { >> new_cachep = cachep; >> + css_put(&memcg->css); >> goto out; >> } >> >> - mem_cgroup_get(memcg); >> atomic_set(&new_cachep->memcg_params->nr_pages , 0); >> >> cachep->memcg_params->memcg_caches[idx] = new_cachep; >> @@ -3449,8 +3451,6 @@ static void memcg_create_cache_work_func(struct >> work_struct *w) >> >> cw = container_of(w, struct create_work, work); >> memcg_create_kmem_cache(cw->memcg, cw->cachep); >> - /* Drop the reference gotten when we enqueued. */ >> - css_put(&cw->memcg->css); >> kfree(cw); >> } > > You are putting references but I do not see any single css_{try}get > here. /me puzzled. >
There are two things being done in this code: First, we acquired a css_ref to make sure that the underlying cgroup would not go away. That is a short lived reference, and it is put as soon as the cache is created. At this point, we acquire a long-lived per-cache memcg reference count to guarantee that the memcg will still be alive. so it is: enqueue: css_get create : memcg_get, css_put destroy: css_put If I understand Li's patch correctly, he is not touching the first css_get, only turning that into the long lived reference (which was not possible before, since that would prevent rmdir). Then he only needs to get rid of the memcg_get, change the memcg_put to css_put, and get rid of the now extra css_put. He is issuing extra css_puts in memcg_create_kmem_cache, but only in failure paths. So the code reads as: * css_get on enqueue (already done, so not shown in patch) * if it fails, css_put * if it succeeds, don't do anything. This is already the long-lived reference count. put it at release time. The code looks correct, and of course, extremely simpler due to the use of a single reference. Li, am I right in my understanding that this is your intention? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
