From: Roman Gushchin <guro@xxxxxx>
Subject: mm: memcg/slab: rework non-root kmem_cache lifecycle management
Currently each charged slab page holds a reference to the cgroup to which
it's charged. Kmem_caches are held by the memcg and are released all
together with the memory cgroup. It means that none of kmem_caches are
released unless at least one reference to the memcg exists, which is very
far from optimal.
Let's rework it in a way that allows releasing individual kmem_caches as
soon as the cgroup is offline, the kmem_cache is empty and there are no
pending allocations.
To make it possible, let's introduce a new percpu refcounter for non-root
kmem caches. The counter is initialized to the percpu mode, and is
switched to the atomic mode during kmem_cache deactivation. The counter
is bumped for every charged page and also for every running allocation.
So the kmem_cache can't be released unless all allocations complete.
To shutdown non-active empty kmem_caches, let's reuse the work queue,
previously used for the kmem_cache deactivation. Once the reference
counter reaches 0, let's schedule an asynchronous kmem_cache release.
* I used the following simple approach to test the performance
(stolen from another patchset by T. Harding):
time find / -name fname-no-exist
echo 2 > /proc/sys/vm/drop_caches
repeat 10 times
Results:
orig patched
real 0m1.455s real 0m1.355s
user 0m0.206s user 0m0.219s
sys 0m0.855s sys 0m0.807s
real 0m1.487s real 0m1.699s
user 0m0.221s user 0m0.256s
sys 0m0.806s sys 0m0.948s
real 0m1.515s real 0m1.505s
user 0m0.183s user 0m0.215s
sys 0m0.876s sys 0m0.858s
real 0m1.291s real 0m1.380s
user 0m0.193s user 0m0.198s
sys 0m0.843s sys 0m0.786s
real 0m1.364s real 0m1.374s
user 0m0.180s user 0m0.182s
sys 0m0.868s sys 0m0.806s
real 0m1.352s real 0m1.312s
user 0m0.201s user 0m0.212s
sys 0m0.820s sys 0m0.761s
real 0m1.302s real 0m1.349s
user 0m0.205s user 0m0.203s
sys 0m0.803s sys 0m0.792s
real 0m1.334s real 0m1.301s
user 0m0.194s user 0m0.201s
sys 0m0.806s sys 0m0.779s
real 0m1.426s real 0m1.434s
user 0m0.216s user 0m0.181s
sys 0m0.824s sys 0m0.864s
real 0m1.350s real 0m1.295s
user 0m0.200s user 0m0.190s
sys 0m0.842s sys 0m0.811s
So it looks like the difference is not noticeable in this test.
[cai@xxxxxx: fix an use-after-free in kmemcg_workfn()]
Link: http://lkml.kernel.org/r/1560977573-10715-1-git-send-email-cai@xxxxxx
Link: http://lkml.kernel.org/r/20190611231813.3148843-9-guro@xxxxxx
Signed-off-by: Roman Gushchin <guro@xxxxxx>
Signed-off-by: Qian Cai <cai@xxxxxx>
Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Andrei Vagin <avagin@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/slab.h | 3 +
mm/memcontrol.c | 50 +++++++++++++++++++-------
mm/slab.h | 44 ++++++-----------------
mm/slab_common.c | 78 +++++++++++++++++++++++------------------
4 files changed, 96 insertions(+), 79 deletions(-)
--- a/include/linux/slab.h~mm-rework-non-root-kmem_cache-lifecycle-management
+++ a/include/linux/slab.h
@@ -16,6 +16,7 @@
#include <linux/overflow.h>
#include <linux/types.h>
#include <linux/workqueue.h>
+#include <linux/percpu-refcount.h>
/*
@@ -152,7 +153,6 @@ int kmem_cache_shrink(struct kmem_cache
void memcg_create_kmem_cache(struct mem_cgroup *, struct kmem_cache *);
void memcg_deactivate_kmem_caches(struct mem_cgroup *);
-void memcg_destroy_kmem_caches(struct mem_cgroup *);
/*
* Please use this macro to create slab caches. Simply specify the
@@ -642,6 +642,7 @@ struct memcg_cache_params {
struct mem_cgroup *memcg;
struct list_head children_node;
struct list_head kmem_caches_node;
+ struct percpu_ref refcnt;
void (*work_fn)(struct kmem_cache *);
union {
--- a/mm/memcontrol.c~mm-rework-non-root-kmem_cache-lifecycle-management
+++ a/mm/memcontrol.c
@@ -2660,12 +2660,13 @@ static void memcg_schedule_kmem_cache_cr
{
struct memcg_kmem_cache_create_work *cw;
+ if (!css_tryget_online(&memcg->css))
+ return;
+
cw = kmalloc(sizeof(*cw), GFP_NOWAIT | __GFP_NOWARN);
if (!cw)
return;
- css_get(&memcg->css);
-
cw->memcg = memcg;
cw->cachep = cachep;
INIT_WORK(&cw->work, memcg_kmem_cache_create_func);
@@ -2700,6 +2701,7 @@ struct kmem_cache *memcg_kmem_get_cache(
{
struct mem_cgroup *memcg;
struct kmem_cache *memcg_cachep;
+ struct memcg_cache_array *arr;
int kmemcg_id;
VM_BUG_ON(!is_root_cache(cachep));
@@ -2707,14 +2709,28 @@ struct kmem_cache *memcg_kmem_get_cache(
if (memcg_kmem_bypass())
return cachep;
- memcg = get_mem_cgroup_from_current();
+ rcu_read_lock();
+
+ if (unlikely(current->active_memcg))
+ memcg = current->active_memcg;
+ else
+ memcg = mem_cgroup_from_task(current);
+
+ if (!memcg || memcg == root_mem_cgroup)
+ goto out_unlock;
+
kmemcg_id = READ_ONCE(memcg->kmemcg_id);
if (kmemcg_id < 0)
- goto out;
+ goto out_unlock;
+
+ arr = rcu_dereference(cachep->memcg_params.memcg_caches);
- memcg_cachep = cache_from_memcg_idx(cachep, kmemcg_id);
- if (likely(memcg_cachep))
- return memcg_cachep;
+ /*
+ * Make sure we will access the up-to-date value. The code updating
+ * memcg_caches issues a write barrier to match the data dependency
+ * barrier inside READ_ONCE() (see memcg_create_kmem_cache()).
+ */
+ memcg_cachep = READ_ONCE(arr->entries[kmemcg_id]);
/*
* If we are in a safe context (can wait, and not in interrupt
@@ -2727,10 +2743,20 @@ struct kmem_cache *memcg_kmem_get_cache(
* memcg_create_kmem_cache, this means no further allocation
* could happen with the slab_mutex held. So it's better to
* defer everything.
+ *
+ * If the memcg is dying or memcg_cache is about to be released,
+ * don't bother creating new kmem_caches. Because memcg_cachep
+ * is ZEROed as the fist step of kmem offlining, we don't need
+ * percpu_ref_tryget_live() here. css_tryget_online() check in
+ * memcg_schedule_kmem_cache_create() will prevent us from
+ * creation of a new kmem_cache.
*/
- memcg_schedule_kmem_cache_create(memcg, cachep);
-out:
- css_put(&memcg->css);
+ if (unlikely(!memcg_cachep))
+ memcg_schedule_kmem_cache_create(memcg, cachep);
+ else if (percpu_ref_tryget(&memcg_cachep->memcg_params.refcnt))
+ cachep = memcg_cachep;
+out_unlock:
+ rcu_read_unlock();
return cachep;
}
@@ -2741,7 +2767,7 @@ out:
void memcg_kmem_put_cache(struct kmem_cache *cachep)
{
if (!is_root_cache(cachep))
- css_put(&cachep->memcg_params.memcg->css);
+ percpu_ref_put(&cachep->memcg_params.refcnt);
}
/**
@@ -3288,7 +3314,7 @@ static void memcg_free_kmem(struct mem_c
memcg_offline_kmem(memcg);
if (memcg->kmem_state == KMEM_ALLOCATED) {
- memcg_destroy_kmem_caches(memcg);
+ WARN_ON(!list_empty(&memcg->kmem_caches));
static_branch_dec(&memcg_kmem_enabled_key);
WARN_ON(page_counter_read(&memcg->kmem));
}
--- a/mm/slab_common.c~mm-rework-non-root-kmem_cache-lifecycle-management
+++ a/mm/slab_common.c
@@ -132,6 +132,8 @@ int __kmem_cache_alloc_bulk(struct kmem_
LIST_HEAD(slab_root_caches);
static DEFINE_SPINLOCK(memcg_kmem_wq_lock);
+static void kmemcg_cache_shutdown(struct percpu_ref *percpu_ref);
+
void slab_init_memcg_params(struct kmem_cache *s)
{
s->memcg_params.root_cache = NULL;
@@ -146,6 +148,12 @@ static int init_memcg_params(struct kmem
struct memcg_cache_array *arr;
if (root_cache) {
+ int ret = percpu_ref_init(&s->memcg_params.refcnt,
+ kmemcg_cache_shutdown,
+ 0, GFP_KERNEL);
+ if (ret)
+ return ret;
+
s->memcg_params.root_cache = root_cache;
INIT_LIST_HEAD(&s->memcg_params.children_node);
INIT_LIST_HEAD(&s->memcg_params.kmem_caches_node);
@@ -171,6 +179,8 @@ static void destroy_memcg_params(struct
{
if (is_root_cache(s))
kvfree(rcu_access_pointer(s->memcg_params.memcg_caches));
+ else
+ percpu_ref_exit(&s->memcg_params.refcnt);
}
static void free_memcg_params(struct rcu_head *rcu)
@@ -226,6 +236,7 @@ void memcg_link_cache(struct kmem_cache
if (is_root_cache(s)) {
list_add(&s->root_caches_node, &slab_root_caches);
} else {
+ css_get(&memcg->css);
s->memcg_params.memcg = memcg;
list_add(&s->memcg_params.children_node,
&s->memcg_params.root_cache->memcg_params.children);
@@ -241,6 +252,7 @@ static void memcg_unlink_cache(struct km
} else {
list_del(&s->memcg_params.children_node);
list_del(&s->memcg_params.kmem_caches_node);
+ css_put(&s->memcg_params.memcg->css);
}
}
#else
@@ -678,7 +690,7 @@ void memcg_create_kmem_cache(struct mem_
}
/*
- * Since readers won't lock (see cache_from_memcg_idx()), we need a
+ * Since readers won't lock (see memcg_kmem_get_cache()), we need a
* barrier here to ensure nobody will see the kmem_cache partially
* initialized.
*/
@@ -701,16 +713,11 @@ static void kmemcg_workfn(struct work_st
get_online_mems();
mutex_lock(&slab_mutex);
-
s->memcg_params.work_fn(s);
-
mutex_unlock(&slab_mutex);
put_online_mems();
put_online_cpus();
-
- /* done, put the ref from kmemcg_cache_deactivate() */
- css_put(&s->memcg_params.memcg->css);
}
static void kmemcg_rcufn(struct rcu_head *head)
@@ -727,10 +734,38 @@ static void kmemcg_rcufn(struct rcu_head
queue_work(memcg_kmem_cache_wq, &s->memcg_params.work);
}
+static void kmemcg_cache_shutdown_fn(struct kmem_cache *s)
+{
+ WARN_ON(shutdown_cache(s));
+}
+
+static void kmemcg_cache_shutdown(struct percpu_ref *percpu_ref)
+{
+ struct kmem_cache *s = container_of(percpu_ref, struct kmem_cache,
+ memcg_params.refcnt);
+ unsigned long flags;
+
+ spin_lock_irqsave(&memcg_kmem_wq_lock, flags);
+ if (s->memcg_params.root_cache->memcg_params.dying)
+ goto unlock;
+
+ s->memcg_params.work_fn = kmemcg_cache_shutdown_fn;
+ INIT_WORK(&s->memcg_params.work, kmemcg_workfn);
+ queue_work(memcg_kmem_cache_wq, &s->memcg_params.work);
+
+unlock:
+ spin_unlock_irqrestore(&memcg_kmem_wq_lock, flags);
+}
+
+static void kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s)
+{
+ __kmemcg_cache_deactivate_after_rcu(s);
+ percpu_ref_kill(&s->memcg_params.refcnt);
+}
+
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))
+ if (WARN_ON_ONCE(is_root_cache(s)))
return;
__kmemcg_cache_deactivate(s);
@@ -744,10 +779,7 @@ static void kmemcg_cache_deactivate(stru
if (s->memcg_params.root_cache->memcg_params.dying)
goto unlock;
- /* pin memcg so that @s doesn't get destroyed in the middle */
- css_get(&s->memcg_params.memcg->css);
-
- s->memcg_params.work_fn = __kmemcg_cache_deactivate_after_rcu;
+ s->memcg_params.work_fn = kmemcg_cache_deactivate_after_rcu;
call_rcu(&s->memcg_params.rcu_head, kmemcg_rcufn);
unlock:
spin_unlock_irq(&memcg_kmem_wq_lock);
@@ -777,28 +809,6 @@ void memcg_deactivate_kmem_caches(struct
}
mutex_unlock(&slab_mutex);
- put_online_mems();
- put_online_cpus();
-}
-
-void memcg_destroy_kmem_caches(struct mem_cgroup *memcg)
-{
- struct kmem_cache *s, *s2;
-
- get_online_cpus();
- get_online_mems();
-
- mutex_lock(&slab_mutex);
- list_for_each_entry_safe(s, s2, &memcg->kmem_caches,
- memcg_params.kmem_caches_node) {
- /*
- * The cgroup is about to be freed and therefore has no charges
- * left. Hence, all its caches must be empty by now.
- */
- BUG_ON(shutdown_cache(s));
- }
- mutex_unlock(&slab_mutex);
-
put_online_mems();
put_online_cpus();
}
--- a/mm/slab.h~mm-rework-non-root-kmem_cache-lifecycle-management
+++ a/mm/slab.h
@@ -248,31 +248,6 @@ static inline const char *cache_name(str
return s->name;
}
-/*
- * Note, we protect with RCU only the memcg_caches array, not per-memcg caches.
- * That said the caller must assure the memcg's cache won't go away by either
- * taking a css reference to the owner cgroup, or holding the slab_mutex.
- */
-static inline struct kmem_cache *
-cache_from_memcg_idx(struct kmem_cache *s, int idx)
-{
- struct kmem_cache *cachep;
- struct memcg_cache_array *arr;
-
- rcu_read_lock();
- arr = rcu_dereference(s->memcg_params.memcg_caches);
-
- /*
- * Make sure we will access the up-to-date value. The code updating
- * memcg_caches issues a write barrier to match this (see
- * memcg_create_kmem_cache()).
- */
- cachep = READ_ONCE(arr->entries[idx]);
- rcu_read_unlock();
-
- return cachep;
-}
-
static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s)
{
if (is_root_cache(s))
@@ -284,14 +259,25 @@ static __always_inline int memcg_charge_
gfp_t gfp, int order,
struct kmem_cache *s)
{
+ int ret;
+
if (is_root_cache(s))
return 0;
- return memcg_kmem_charge_memcg(page, gfp, order, s->memcg_params.memcg);
+
+ ret = memcg_kmem_charge_memcg(page, gfp, order, s->memcg_params.memcg);
+ if (ret)
+ return ret;
+
+ percpu_ref_get_many(&s->memcg_params.refcnt, 1 << order);
+
+ return 0;
}
static __always_inline void memcg_uncharge_slab(struct page *page, int order,
struct kmem_cache *s)
{
+ if (!is_root_cache(s))
+ percpu_ref_put_many(&s->memcg_params.refcnt, 1 << order);
memcg_kmem_uncharge(page, order);
}
@@ -323,12 +309,6 @@ static inline const char *cache_name(str
return s->name;
}
-static inline struct kmem_cache *
-cache_from_memcg_idx(struct kmem_cache *s, int idx)
-{
- return NULL;
-}
-
static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s)
{
return s;
_
