Commit 0c7c1bed authored by Kirill Tkhai's avatar Kirill Tkhai Committed by Linus Torvalds

mm: make counting of list_lru_one::nr_items lockless

During the reclaiming slab of a memcg, shrink_slab iterates over all
registered shrinkers in the system, and tries to count and consume
objects related to the cgroup.  In case of memory pressure, this behaves
bad: I observe high system time and time spent in list_lru_count_one()
for many processes on RHEL7 kernel.

This patch makes list_lru_node::memcg_lrus rcu protected, that allows to
skip taking spinlock in list_lru_count_one().

Shakeel Butt with the patch observes significant perf graph change.  He
says:

========================================================================
Setup: running a fork-bomb in a memcg of 200MiB on a 8GiB and 4 vcpu
VM and recording the trace with 'perf record -g -a'.

The trace without the patch:

+  34.19%     fb.sh  [kernel.kallsyms]  [k] queued_spin_lock_slowpath
+  30.77%     fb.sh  [kernel.kallsyms]  [k] _raw_spin_lock
+   3.53%     fb.sh  [kernel.kallsyms]  [k] list_lru_count_one
+   2.26%     fb.sh  [kernel.kallsyms]  [k] super_cache_count
+   1.68%     fb.sh  [kernel.kallsyms]  [k] shrink_slab
+   0.59%     fb.sh  [kernel.kallsyms]  [k] down_read_trylock
+   0.48%     fb.sh  [kernel.kallsyms]  [k] _raw_spin_unlock_irqrestore
+   0.38%     fb.sh  [kernel.kallsyms]  [k] shrink_node_memcg
+   0.32%     fb.sh  [kernel.kallsyms]  [k] queue_work_on
+   0.26%     fb.sh  [kernel.kallsyms]  [k] count_shadow_nodes

With the patch:

+   0.16%     swapper  [kernel.kallsyms]    [k] default_idle
+   0.13%     oom_reaper  [kernel.kallsyms]    [k] mutex_spin_on_owner
+   0.05%     perf  [kernel.kallsyms]    [k] copy_user_generic_string
+   0.05%     init.real  [kernel.kallsyms]    [k] wait_consider_task
+   0.05%     kworker/0:0  [kernel.kallsyms]    [k] finish_task_switch
+   0.04%     kworker/2:1  [kernel.kallsyms]    [k] finish_task_switch
+   0.04%     kworker/3:1  [kernel.kallsyms]    [k] finish_task_switch
+   0.04%     kworker/1:0  [kernel.kallsyms]    [k] finish_task_switch
+   0.03%     binary  [kernel.kallsyms]    [k] copy_page
========================================================================

Thanks Shakeel for the testing.

[ktkhai@virtuozzo.com: v2]
  Link: http://lkml.kernel.org/r/151203869520.3915.2587549826865799173.stgit@localhost.localdomain
Link: http://lkml.kernel.org/r/150583358557.26700.8490036563698102569.stgit@localhost.localdomainSigned-off-by: default avatarKirill Tkhai <ktkhai@virtuozzo.com>
Tested-by: default avatarShakeel Butt <shakeelb@google.com>
Acked-by: default avatarVladimir Davydov <vdavydov.dev@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f5c754d6
......@@ -32,6 +32,7 @@ struct list_lru_one {
};
struct list_lru_memcg {
struct rcu_head rcu;
/* array of per cgroup lists, indexed by memcg_cache_id */
struct list_lru_one *lru[0];
};
......@@ -43,7 +44,7 @@ struct list_lru_node {
struct list_lru_one lru;
#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
/* for cgroup aware lrus points to per cgroup lists, otherwise NULL */
struct list_lru_memcg *memcg_lrus;
struct list_lru_memcg __rcu *memcg_lrus;
#endif
long nr_items;
} ____cacheline_aligned_in_smp;
......
......@@ -52,14 +52,15 @@ 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)
{
struct list_lru_memcg *memcg_lrus;
/*
* The lock protects the array of per cgroup lists from relocation
* (see memcg_update_list_lru_node).
* Either lock or RCU 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];
memcg_lrus = rcu_dereference_check(nlru->memcg_lrus,
lockdep_is_held(&nlru->lock));
if (memcg_lrus && idx >= 0)
return memcg_lrus->lru[idx];
return &nlru->lru;
}
......@@ -168,10 +169,10 @@ static unsigned long __list_lru_count_one(struct list_lru *lru,
struct list_lru_one *l;
unsigned long count;
spin_lock(&nlru->lock);
rcu_read_lock();
l = list_lru_from_memcg_idx(nlru, memcg_idx);
count = l->nr_items;
spin_unlock(&nlru->lock);
rcu_read_unlock();
return count;
}
......@@ -324,24 +325,41 @@ 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)
{
struct list_lru_memcg *memcg_lrus;
int size = memcg_nr_cache_ids;
nlru->memcg_lrus = kvmalloc(size * sizeof(void *), GFP_KERNEL);
if (!nlru->memcg_lrus)
memcg_lrus = kvmalloc(sizeof(*memcg_lrus) +
size * sizeof(void *), GFP_KERNEL);
if (!memcg_lrus)
return -ENOMEM;
if (__memcg_init_list_lru_node(nlru->memcg_lrus, 0, size)) {
kvfree(nlru->memcg_lrus);
if (__memcg_init_list_lru_node(memcg_lrus, 0, size)) {
kvfree(memcg_lrus);
return -ENOMEM;
}
RCU_INIT_POINTER(nlru->memcg_lrus, memcg_lrus);
return 0;
}
static void memcg_destroy_list_lru_node(struct list_lru_node *nlru)
{
__memcg_destroy_list_lru_node(nlru->memcg_lrus, 0, memcg_nr_cache_ids);
kvfree(nlru->memcg_lrus);
struct list_lru_memcg *memcg_lrus;
/*
* This is called when shrinker has already been unregistered,
* and nobody can use it. So, there is no need to use kvfree_rcu().
*/
memcg_lrus = rcu_dereference_protected(nlru->memcg_lrus, true);
__memcg_destroy_list_lru_node(memcg_lrus, 0, memcg_nr_cache_ids);
kvfree(memcg_lrus);
}
static void kvfree_rcu(struct rcu_head *head)
{
struct list_lru_memcg *mlru;
mlru = container_of(head, struct list_lru_memcg, rcu);
kvfree(mlru);
}
static int memcg_update_list_lru_node(struct list_lru_node *nlru,
......@@ -351,8 +369,9 @@ static int memcg_update_list_lru_node(struct list_lru_node *nlru,
BUG_ON(old_size > new_size);
old = nlru->memcg_lrus;
new = kvmalloc(new_size * sizeof(void *), GFP_KERNEL);
old = rcu_dereference_protected(nlru->memcg_lrus,
lockdep_is_held(&list_lrus_mutex));
new = kvmalloc(sizeof(*new) + new_size * sizeof(void *), GFP_KERNEL);
if (!new)
return -ENOMEM;
......@@ -361,29 +380,33 @@ static int memcg_update_list_lru_node(struct list_lru_node *nlru,
return -ENOMEM;
}
memcpy(new, old, old_size * sizeof(void *));
memcpy(&new->lru, &old->lru, old_size * sizeof(void *));
/*
* The lock guarantees that we won't race with a reader
* (see list_lru_from_memcg_idx).
* The locking below allows readers that hold nlru->lock avoid taking
* rcu_read_lock (see list_lru_from_memcg_idx).
*
* 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);
nlru->memcg_lrus = new;
rcu_assign_pointer(nlru->memcg_lrus, new);
spin_unlock_irq(&nlru->lock);
kvfree(old);
call_rcu(&old->rcu, kvfree_rcu);
return 0;
}
static void memcg_cancel_update_list_lru_node(struct list_lru_node *nlru,
int old_size, int new_size)
{
struct list_lru_memcg *memcg_lrus;
memcg_lrus = rcu_dereference_protected(nlru->memcg_lrus,
lockdep_is_held(&list_lrus_mutex));
/* do not bother shrinking the array back to the old size, because we
* cannot handle allocation failures here */
__memcg_destroy_list_lru_node(nlru->memcg_lrus, old_size, new_size);
__memcg_destroy_list_lru_node(memcg_lrus, old_size, new_size);
}
static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
......
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