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Subject[PATCH v2 2/6] mm: generalize postponed non-root kmem_cache deactivation
Date
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 reparenting, but requires some generalization.

Let's decouple all infrastructure (rcu callback, work callback)
from the SLUB-specific code, so it can be used with SLAB as well.

Also, let's rename some functions to make the code look simpler.
All SLAB/SLUB-specific functions start with "__". Remove "deact_"
prefix from the corresponding struct fields.

Here is the graph of a new calling scheme:
kmemcg_cache_deactivate()
__kmemcg_cache_deactivate() SLAB/SLUB-specific
kmemcg_schedule_work_after_rcu() rcu
kmemcg_after_rcu_workfn() work
kmemcg_cache_deactivate_after_rcu()
__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_deactivate_rcufn SLUB-only, rcu
kmemcg_deactivate_workfn SLUB-only, work
kmemcg_cache_deact_after_rcu() SLUB-only

Signed-off-by: Roman Gushchin <guro@fb.com>
---
include/linux/slab.h | 6 ++---
mm/slab.c | 4 +++
mm/slab.h | 3 ++-
mm/slab_common.c | 62 ++++++++++++++++++++------------------------
mm/slub.c | 8 +-----
5 files changed, 38 insertions(+), 45 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 9449b19c5f10..47923c173f30 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -642,10 +642,10 @@ struct memcg_cache_params {
struct list_head children_node;
struct list_head kmem_caches_node;

- void (*deact_fn)(struct kmem_cache *);
+ void (*work_fn)(struct kmem_cache *);
union {
- struct rcu_head deact_rcu_head;
- struct work_struct deact_work;
+ struct rcu_head rcu_head;
+ struct work_struct work;
};
};
};
diff --git a/mm/slab.c b/mm/slab.c
index 57a332f524cf..14466a73d057 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2317,6 +2317,10 @@ 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 6a562ca72bca..4a261c97c138 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;
@@ -291,7 +292,7 @@ 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 (*deact_fn)(struct kmem_cache *));
+ void (*work_fn)(struct kmem_cache *));

#else /* CONFIG_MEMCG_KMEM */

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 6e00bdf8618d..4e5b4292a763 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -691,17 +691,18 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
put_online_cpus();
}

-static void kmemcg_deactivate_workfn(struct work_struct *work)
+static void kmemcg_after_rcu_workfn(struct work_struct *work)
{
struct kmem_cache *s = container_of(work, struct kmem_cache,
- memcg_params.deact_work);
+ memcg_params.work);

get_online_cpus();
get_online_mems();

mutex_lock(&slab_mutex);

- s->memcg_params.deact_fn(s);
+ s->memcg_params.work_fn(s);
+ s->memcg_params.work_fn = NULL;

mutex_unlock(&slab_mutex);

@@ -712,37 +713,28 @@ static void kmemcg_deactivate_workfn(struct work_struct *work)
css_put(&s->memcg_params.memcg->css);
}

-static void kmemcg_deactivate_rcufn(struct rcu_head *head)
+/*
+ * We need to grab blocking locks. Bounce to ->work. The
+ * work item shares the space with the RCU head and can't be
+ * initialized eariler.
+*/
+static void kmemcg_schedule_work_after_rcu(struct rcu_head *head)
{
struct kmem_cache *s = container_of(head, struct kmem_cache,
- memcg_params.deact_rcu_head);
+ memcg_params.rcu_head);

- /*
- * We need to grab blocking locks. Bounce to ->deact_work. The
- * work item shares the space with the RCU head and can't be
- * initialized eariler.
- */
- INIT_WORK(&s->memcg_params.deact_work, kmemcg_deactivate_workfn);
- queue_work(memcg_kmem_cache_wq, &s->memcg_params.deact_work);
+ INIT_WORK(&s->memcg_params.work, kmemcg_after_rcu_workfn);
+ 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
- * @deact_fn: deactivation function to call
- *
- * Schedule @deact_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 @deact_fn is finished. This is to be used from
- * __kmemcg_cache_deactivate().
- */
-void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
- void (*deact_fn)(struct kmem_cache *))
+static void kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s)
{
- if (WARN_ON_ONCE(is_root_cache(s)) ||
- WARN_ON_ONCE(s->memcg_params.deact_fn))
- return;
+ __kmemcg_cache_deactivate_after_rcu(s);
+}
+
+static void kmemcg_cache_deactivate(struct kmem_cache *s)
+{
+ __kmemcg_cache_deactivate(s);

if (s->memcg_params.root_cache->memcg_params.dying)
return;
@@ -750,8 +742,9 @@ void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
/* pin memcg so that @s doesn't get destroyed in the middle */
css_get(&s->memcg_params.memcg->css);

- s->memcg_params.deact_fn = deact_fn;
- call_rcu(&s->memcg_params.deact_rcu_head, kmemcg_deactivate_rcufn);
+ WARN_ON_ONCE(s->memcg_params.work_fn);
+ s->memcg_params.work_fn = kmemcg_cache_deactivate_after_rcu;
+ call_rcu(&s->memcg_params.rcu_head, kmemcg_schedule_work_after_rcu);
}

void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
@@ -773,7 +766,7 @@ 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);
@@ -866,11 +859,12 @@ 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();
+#ifndef CONFIG_SLOB
+ rcu_barrier();
+#endif

/*
* SLAB and SLUB create memcg kmem_caches through workqueue and SLUB
diff --git a/mm/slub.c b/mm/slub.c
index 2b9244529d76..195f61785c7d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4033,7 +4033,7 @@ 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.
@@ -4059,12 +4059,6 @@ 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
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