[PATCH v6 04/10] mm: generalize postponed non-root kmem_cache deactivation

[Roman Gushchin]

Currently SLUB uses a work scheduled after an RCU grace period
to deactivate a non-root kmem_cache. This mechanism can be reused
for kmem_caches release, but requires generalization for SLAB
case.

Introduce kmemcg_cache_deactivate() function, which calls
allocator-specific __kmem_cache_deactivate() and schedules
execution of __kmem_cache_deactivate_after_rcu() with all
necessary locks in a worker context after an rcu grace period.

Here is the new calling scheme:
  kmemcg_cache_deactivate()
    __kmemcg_cache_deactivate()                  SLAB/SLUB-specific
    kmemcg_rcufn()                               rcu
      kmemcg_workfn()                            work
        __kmemcg_cache_deactivate_after_rcu()    SLAB/SLUB-specific

instead of:
  __kmemcg_cache_deactivate()                    SLAB/SLUB-specific
    slab_deactivate_memcg_cache_rcu_sched()      SLUB-only
      kmemcg_rcufn()                             rcu
        kmemcg_workfn()                          work
          kmemcg_cache_deact_after_rcu()         SLUB-only

For consistency, all allocator-specific functions start with "__".

Signed-off-by: Roman Gushchin <guro@xxxxxx>
---
 mm/slab.c        |  4 ++++
 mm/slab.h        |  3 +--
 mm/slab_common.c | 27 ++++++++-------------------
 mm/slub.c        |  8 +-------
 4 files changed, 14 insertions(+), 28 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index a4091f8b3655..4b865393ebb4 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2252,6 +2252,10 @@ void __kmemcg_cache_deactivate(struct kmem_cache *cachep)
 {
 	__kmem_cache_shrink(cachep);
 }
+
+void __kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s)
+{
+}
 #endif
 
 int __kmem_cache_shutdown(struct kmem_cache *cachep)
diff --git a/mm/slab.h b/mm/slab.h
index 8ff90f42548a..d35d85794247 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -172,6 +172,7 @@ int __kmem_cache_shutdown(struct kmem_cache *);
 void __kmem_cache_release(struct kmem_cache *);
 int __kmem_cache_shrink(struct kmem_cache *);
 void __kmemcg_cache_deactivate(struct kmem_cache *s);
+void __kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s);
 void slab_kmem_cache_release(struct kmem_cache *);
 
 struct seq_file;
@@ -291,8 +292,6 @@ static __always_inline void memcg_uncharge_slab(struct page *page, int order,
 
 extern void slab_init_memcg_params(struct kmem_cache *);
 extern void memcg_link_cache(struct kmem_cache *s, struct mem_cgroup *memcg);
-extern void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
-				void (*work_fn)(struct kmem_cache *));
 
 #else /* CONFIG_MEMCG_KMEM */
 
diff --git a/mm/slab_common.c b/mm/slab_common.c
index d019ee66bdc4..09b26673b63f 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -709,7 +709,7 @@ static void kmemcg_workfn(struct work_struct *work)
 	put_online_mems();
 	put_online_cpus();
 
-	/* done, put the ref from slab_deactivate_memcg_cache_rcu_sched() */
+	/* done, put the ref from kmemcg_cache_deactivate() */
 	css_put(&s->memcg_params.memcg->css);
 }
 
@@ -727,31 +727,21 @@ static void kmemcg_rcufn(struct rcu_head *head)
 	queue_work(memcg_kmem_cache_wq, &s->memcg_params.work);
 }
 
-/**
- * slab_deactivate_memcg_cache_rcu_sched - schedule deactivation after a
- *					   sched RCU grace period
- * @s: target kmem_cache
- * @work_fn: deactivation function to call
- *
- * Schedule @work_fn to be invoked with online cpus, mems and slab_mutex
- * held after a sched RCU grace period.  The slab is guaranteed to stay
- * alive until @work_fn is finished.  This is to be used from
- * __kmemcg_cache_deactivate().
- */
-void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
-					   void (*work_fn)(struct kmem_cache *))
+static void kmemcg_cache_deactivate(struct kmem_cache *s)
 {
 	if (WARN_ON_ONCE(is_root_cache(s)) ||
 	    WARN_ON_ONCE(s->memcg_params.work_fn))
 		return;
 
+	__kmemcg_cache_deactivate(s);
+
 	if (s->memcg_params.root_cache->memcg_params.dying)
 		return;
 
 	/* pin memcg so that @s doesn't get destroyed in the middle */
 	css_get(&s->memcg_params.memcg->css);
 
-	s->memcg_params.work_fn = work_fn;
+	s->memcg_params.work_fn = __kmemcg_cache_deactivate_after_rcu;
 	call_rcu(&s->memcg_params.rcu_head, kmemcg_rcufn);
 }
 
@@ -774,7 +764,7 @@ void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
 		if (!c)
 			continue;
 
-		__kmemcg_cache_deactivate(c);
+		kmemcg_cache_deactivate(c);
 		arr->entries[idx] = NULL;
 	}
 	mutex_unlock(&slab_mutex);
@@ -867,11 +857,10 @@ static void flush_memcg_workqueue(struct kmem_cache *s)
 	mutex_unlock(&slab_mutex);
 
 	/*
-	 * SLUB deactivates the kmem_caches through call_rcu. Make
+	 * SLAB and SLUB deactivate the kmem_caches through call_rcu. Make
 	 * sure all registered rcu callbacks have been invoked.
 	 */
-	if (IS_ENABLED(CONFIG_SLUB))
-		rcu_barrier();
+	rcu_barrier();
 
 	/*
 	 * SLAB and SLUB create memcg kmem_caches through workqueue and SLUB
diff --git a/mm/slub.c b/mm/slub.c
index 9cb2eef62a37..ae3b1e49ecec 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4022,7 +4022,7 @@ int __kmem_cache_shrink(struct kmem_cache *s)
 }
 
 #ifdef CONFIG_MEMCG
-static void kmemcg_cache_deact_after_rcu(struct kmem_cache *s)
+void __kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s)
 {
 	/*
 	 * Called with all the locks held after a sched RCU grace period.
@@ -4048,12 +4048,6 @@ void __kmemcg_cache_deactivate(struct kmem_cache *s)
 	 */
 	slub_set_cpu_partial(s, 0);
 	s->min_partial = 0;
-
-	/*
-	 * s->cpu_partial is checked locklessly (see put_cpu_partial), so
-	 * we have to make sure the change is visible before shrinking.
-	 */
-	slab_deactivate_memcg_cache_rcu_sched(s, kmemcg_cache_deact_after_rcu);
 }
 #endif	/* CONFIG_MEMCG */
 
-- 
2.20.1