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Subject[PATCH v7 03/10] 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 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@fb.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
---
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 7ef695b91919..dc83583ee9dd 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;
@@ -290,8 +291,6 @@ 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 99489d82ba78..5e7638f495d1 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -708,7 +708,7 @@ 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);
}

@@ -726,31 +726,21 @@ 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);
}

@@ -773,7 +763,7 @@ 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 +856,10 @@ 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 */

--
2.21.0
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