Now, the only reason to keep kmemcg_id till css free is list_lru, which
uses it to distribute elements between per-memcg lists. However, it can
be easily sorted out - we only need to change kmemcg_id of an offline
cgroup to its parent's id, making further list_lru_add()'s add elements
to the parent's list, and then move all elements from the offline
cgroup's list to the one of its parent. It will work, because a racing
list_lru_del() does not need to know the list it is deleting the element
from. It can decrement the wrong nr_items counter though, but the
ongoing reparenting will fix it. After list_lru reparenting is done we
are free to release kmemcg_id saving a valuable slot in a per-memcg
array for new cgroups.
Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
---
include/linux/list_lru.h | 3 ++-
mm/list_lru.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
mm/memcontrol.c | 39 ++++++++++++++++++++++++++++++++++-----
mm/vmscan.c | 2 +-
4 files changed, 80 insertions(+), 10 deletions(-)
diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index 7edf9c9ab9eb..2a6b9947aaa3 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -26,7 +26,7 @@ enum lru_status {
struct list_lru_one {
struct list_head list;
- /* kept as signed so we can catch imbalance bugs */
+ /* may become negative during memcg reparenting */
long nr_items;
};
@@ -62,6 +62,7 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
#define list_lru_init_memcg(lru) __list_lru_init((lru), true, NULL)
int memcg_update_all_list_lrus(int num_memcgs);
+void memcg_drain_all_list_lrus(int src_idx, int dst_idx);
/**
* list_lru_add: add an element to the lru list's tail
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 8d9d168c6c38..909eca2c820e 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -100,7 +100,6 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item)
spin_lock(&nlru->lock);
l = list_lru_from_kmem(nlru, item);
- WARN_ON_ONCE(l->nr_items < 0);
if (list_empty(item)) {
list_add_tail(item, &l->list);
l->nr_items++;
@@ -123,7 +122,6 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item)
if (!list_empty(item)) {
list_del_init(item);
l->nr_items--;
- WARN_ON_ONCE(l->nr_items < 0);
spin_unlock(&nlru->lock);
return true;
}
@@ -156,7 +154,6 @@ static unsigned long __list_lru_count_one(struct list_lru *lru,
spin_lock(&nlru->lock);
l = list_lru_from_memcg_idx(nlru, memcg_idx);
- WARN_ON_ONCE(l->nr_items < 0);
count = l->nr_items;
spin_unlock(&nlru->lock);
@@ -458,6 +455,49 @@ fail:
memcg_cancel_update_list_lru(lru, old_size, new_size);
goto out;
}
+
+static void memcg_drain_list_lru_node(struct list_lru_node *nlru,
+ int src_idx, int dst_idx)
+{
+ struct list_lru_one *src, *dst;
+
+ /*
+ * Since list_lru_{add,del} may be called under an IRQ-safe lock,
+ * we have to use IRQ-safe primitives here to avoid deadlock.
+ */
+ spin_lock_irq(&nlru->lock);
+
+ src = list_lru_from_memcg_idx(nlru, src_idx);
+ dst = list_lru_from_memcg_idx(nlru, dst_idx);
+
+ list_splice_init(&src->list, &dst->list);
+ dst->nr_items += src->nr_items;
+ src->nr_items = 0;
+
+ spin_unlock_irq(&nlru->lock);
+}
+
+static void memcg_drain_list_lru(struct list_lru *lru,
+ int src_idx, int dst_idx)
+{
+ int i;
+
+ if (!list_lru_memcg_aware(lru))
+ return;
+
+ for (i = 0; i < nr_node_ids; i++)
+ memcg_drain_list_lru_node(&lru->node[i], src_idx, dst_idx);
+}
+
+void memcg_drain_all_list_lrus(int src_idx, int dst_idx)
+{
+ struct list_lru *lru;
+
+ mutex_lock(&list_lrus_mutex);
+ list_for_each_entry(lru, &list_lrus, list)
+ memcg_drain_list_lru(lru, src_idx, dst_idx);
+ mutex_unlock(&list_lrus_mutex);
+}
#else
static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
{
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b82ddb68ffd6..850e1fdf3ea9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -347,6 +347,7 @@ struct mem_cgroup {
#if defined(CONFIG_MEMCG_KMEM)
/* Index in the kmem_cache->memcg_params.memcg_caches array */
int kmemcg_id;
+ bool kmem_acct_activated;
bool kmem_acct_active;
#endif
@@ -608,14 +609,10 @@ void memcg_put_cache_ids(void)
struct static_key memcg_kmem_enabled_key;
EXPORT_SYMBOL(memcg_kmem_enabled_key);
-static void memcg_free_cache_id(int id);
-
static void disarm_kmem_keys(struct mem_cgroup *memcg)
{
- if (memcg->kmemcg_id >= 0) {
+ if (memcg->kmem_acct_activated)
static_key_slow_dec(&memcg_kmem_enabled_key);
- memcg_free_cache_id(memcg->kmemcg_id);
- }
/*
* This check can't live in kmem destruction function,
* since the charges will outlive the cgroup
@@ -3331,6 +3328,7 @@ static int memcg_activate_kmem(struct mem_cgroup *memcg,
int memcg_id;
BUG_ON(memcg->kmemcg_id >= 0);
+ BUG_ON(memcg->kmem_acct_activated);
BUG_ON(memcg->kmem_acct_active);
/*
@@ -3374,6 +3372,7 @@ static int memcg_activate_kmem(struct mem_cgroup *memcg,
* patched.
*/
memcg->kmemcg_id = memcg_id;
+ memcg->kmem_acct_activated = true;
memcg->kmem_acct_active = true;
out:
return err;
@@ -4052,6 +4051,10 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
static void memcg_deactivate_kmem(struct mem_cgroup *memcg)
{
+ struct cgroup_subsys_state *css;
+ struct mem_cgroup *parent, *child;
+ int kmemcg_id;
+
if (!memcg->kmem_acct_active)
return;
@@ -4064,6 +4067,32 @@ static void memcg_deactivate_kmem(struct mem_cgroup *memcg)
memcg->kmem_acct_active = false;
memcg_deactivate_kmem_caches(memcg);
+
+ kmemcg_id = memcg->kmemcg_id;
+ BUG_ON(kmemcg_id < 0);
+
+ parent = parent_mem_cgroup(memcg);
+ if (!parent)
+ parent = root_mem_cgroup;
+
+ /*
+ * Change kmemcg_id of this cgroup and all its descendants to the
+ * parent's id, and then move all entries from this cgroup's list_lrus
+ * to ones of the parent. After we have finished, all list_lrus
+ * corresponding to this cgroup are guaranteed to remain empty. The
+ * ordering is imposed by list_lru_node->lock taken by
+ * memcg_drain_all_list_lrus().
+ */
+ css_for_each_descendant_pre(css, &memcg->css) {
+ child = mem_cgroup_from_css(css);
+ BUG_ON(child->kmemcg_id != kmemcg_id);
+ child->kmemcg_id = parent->kmemcg_id;
+ if (!memcg->use_hierarchy)
+ break;
+ }
+ memcg_drain_all_list_lrus(kmemcg_id, parent->kmemcg_id);
+
+ memcg_free_cache_id(kmemcg_id);
}
static void memcg_destroy_kmem(struct mem_cgroup *memcg)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 87ef846d5709..16f3e45742d6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -377,7 +377,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
struct shrinker *shrinker;
unsigned long freed = 0;
- if (memcg_cache_id(memcg) < 0)
+ if (memcg && !memcg_kmem_is_active(memcg))
return 0;
if (nr_scanned == 0)
--
1.7.10.4
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