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

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.localdomain


Signed-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

include/linux/list_lru.h

+2 −1
Original line number Diff line number Diff line
@@ -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;

mm/list_lru.c

+45 −22
Original line number Diff line number Diff line
@@ -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)