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Subject[PATCH] mm/list_lru: replace spinlock with RCU in __list_lru_count_one
Date
when reclaim memory, shink_slab will take lots of time even if
no memory is reclaimed, since list_lru_count_one called by it
needs to take a spinlock

try to optimize it by replacing spinlock with RCU in
__list_lru_count_one

$dd if=aaa of=bbb bs=1k count=3886080
$rm -f bbb
$time echo 100000000 >/cgroup/memory/test/memory.limit_in_bytes

Before: 0m0.415s ===> after: 0m0.395s

Signed-off-by: Li RongQing <lirongqing@baidu.com>
---
include/linux/list_lru.h | 2 ++
mm/list_lru.c | 69 ++++++++++++++++++++++++++++++++++--------------
2 files changed, 51 insertions(+), 20 deletions(-)

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index bb8129a3474d..ae472538038e 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -29,6 +29,7 @@ struct list_lru_one {
struct list_head list;
/* may become negative during memcg reparenting */
long nr_items;
+ struct rcu_head rcu;
};

struct list_lru_memcg {
@@ -46,6 +47,7 @@ struct list_lru_node {
struct list_lru_memcg *memcg_lrus;
#endif
long nr_items;
+ struct rcu_head rcu;
} ____cacheline_aligned_in_smp;

struct list_lru {
diff --git a/mm/list_lru.c b/mm/list_lru.c
index fd41e969ede5..4c58ed861729 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -52,13 +52,13 @@ static inline bool list_lru_memcg_aware(struct list_lru *lru)
static inline struct list_lru_one *
list_lru_from_memcg_idx(struct list_lru_node *nlru, int idx)
{
- /*
- * The lock protects the array of per cgroup lists from relocation
- * (see memcg_update_list_lru_node).
- */
- lockdep_assert_held(&nlru->lock);
- if (nlru->memcg_lrus && idx >= 0)
- return nlru->memcg_lrus->lru[idx];
+ struct list_lru_memcg *tmp;
+
+ WARN_ON_ONCE(!rcu_read_lock_held());
+
+ tmp = rcu_dereference(nlru->memcg_lrus);
+ if (tmp && idx >= 0)
+ return rcu_dereference(tmp->lru[idx]);

return &nlru->lru;
}
@@ -113,14 +113,17 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item)
struct list_lru_one *l;

spin_lock(&nlru->lock);
+ rcu_read_lock();
if (list_empty(item)) {
l = list_lru_from_kmem(nlru, item);
list_add_tail(item, &l->list);
l->nr_items++;
nlru->nr_items++;
+ rcu_read_unlock();
spin_unlock(&nlru->lock);
return true;
}
+ rcu_read_unlock();
spin_unlock(&nlru->lock);
return false;
}
@@ -133,14 +136,17 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item)
struct list_lru_one *l;

spin_lock(&nlru->lock);
+ rcu_read_lock();
if (!list_empty(item)) {
l = list_lru_from_kmem(nlru, item);
list_del_init(item);
l->nr_items--;
nlru->nr_items--;
+ rcu_read_unlock();
spin_unlock(&nlru->lock);
return true;
}
+ rcu_read_unlock();
spin_unlock(&nlru->lock);
return false;
}
@@ -166,12 +172,13 @@ static unsigned long __list_lru_count_one(struct list_lru *lru,
{
struct list_lru_node *nlru = &lru->node[nid];
struct list_lru_one *l;
- unsigned long count;
+ unsigned long count = 0;

- spin_lock(&nlru->lock);
+ rcu_read_lock();
l = list_lru_from_memcg_idx(nlru, memcg_idx);
- count = l->nr_items;
- spin_unlock(&nlru->lock);
+ if (l)
+ count = l->nr_items;
+ rcu_read_unlock();

return count;
}
@@ -204,6 +211,7 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx,
unsigned long isolated = 0;

spin_lock(&nlru->lock);
+ rcu_read_lock();
l = list_lru_from_memcg_idx(nlru, memcg_idx);
restart:
list_for_each_safe(item, n, &l->list) {
@@ -250,6 +258,7 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx,
}
}

+ rcu_read_unlock();
spin_unlock(&nlru->lock);
return isolated;
}
@@ -296,9 +305,14 @@ static void __memcg_destroy_list_lru_node(struct list_lru_memcg *memcg_lrus,
int begin, int end)
{
int i;
+ struct list_lru_one *tmp;

- for (i = begin; i < end; i++)
- kfree(memcg_lrus->lru[i]);
+ for (i = begin; i < end; i++) {
+ tmp = memcg_lrus->lru[i];
+ rcu_assign_pointer(memcg_lrus->lru[i], NULL);
+ if (tmp)
+ kfree_rcu(tmp, rcu);
+ }
}

static int __memcg_init_list_lru_node(struct list_lru_memcg *memcg_lrus,
@@ -314,7 +328,7 @@ static int __memcg_init_list_lru_node(struct list_lru_memcg *memcg_lrus,
goto fail;

init_one_lru(l);
- memcg_lrus->lru[i] = l;
+ rcu_assign_pointer(memcg_lrus->lru[i], l);
}
return 0;
fail:
@@ -325,25 +339,37 @@ static int __memcg_init_list_lru_node(struct list_lru_memcg *memcg_lrus,
static int memcg_init_list_lru_node(struct list_lru_node *nlru)
{
int size = memcg_nr_cache_ids;
+ struct list_lru_memcg *tmp;

- nlru->memcg_lrus = kvmalloc(size * sizeof(void *), GFP_KERNEL);
- if (!nlru->memcg_lrus)
+ tmp = kvmalloc(size * sizeof(void *), GFP_KERNEL);
+ if (!tmp)
return -ENOMEM;

- if (__memcg_init_list_lru_node(nlru->memcg_lrus, 0, size)) {
- kvfree(nlru->memcg_lrus);
+ if (__memcg_init_list_lru_node(tmp, 0, size)) {
+ kvfree(tmp);
return -ENOMEM;
}

+ rcu_assign_pointer(nlru->memcg_lrus, tmp);
+
return 0;
}

-static void memcg_destroy_list_lru_node(struct list_lru_node *nlru)
+static void memcg_destroy_list_lru_node_rcu(struct rcu_head *rcu)
{
+ struct list_lru_node *nlru;
+
+ nlru = container_of(rcu, struct list_lru_node, rcu);
+
__memcg_destroy_list_lru_node(nlru->memcg_lrus, 0, memcg_nr_cache_ids);
kvfree(nlru->memcg_lrus);
}

+static void memcg_destroy_list_lru_node(struct list_lru_node *nlru)
+{
+ call_rcu(&nlru->rcu, memcg_destroy_list_lru_node_rcu);
+}
+
static int memcg_update_list_lru_node(struct list_lru_node *nlru,
int old_size, int new_size)
{
@@ -371,9 +397,10 @@ static int memcg_update_list_lru_node(struct list_lru_node *nlru,
* we have to use IRQ-safe primitives here to avoid deadlock.
*/
spin_lock_irq(&nlru->lock);
- nlru->memcg_lrus = new;
+ rcu_assign_pointer(nlru->memcg_lrus, new);
spin_unlock_irq(&nlru->lock);

+ synchronize_rcu();
kvfree(old);
return 0;
}
@@ -487,6 +514,7 @@ static void memcg_drain_list_lru_node(struct list_lru_node *nlru,
* we have to use IRQ-safe primitives here to avoid deadlock.
*/
spin_lock_irq(&nlru->lock);
+ rcu_read_lock();

src = list_lru_from_memcg_idx(nlru, src_idx);
dst = list_lru_from_memcg_idx(nlru, dst_idx);
@@ -495,6 +523,7 @@ static void memcg_drain_list_lru_node(struct list_lru_node *nlru,
dst->nr_items += src->nr_items;
src->nr_items = 0;

+ rcu_read_unlock();
spin_unlock_irq(&nlru->lock);
}

--
2.11.0
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