linux/mm/list_lru.c
Yang Shi 8199be001a mm: list_lru: set shrinker map bit when child nr_items is not zero
When investigating a slab cache bloat problem, significant amount of
negative dentry cache was seen, but confusingly they neither got shrunk
by reclaimer (the host has very tight memory) nor be shrunk by dropping
cache.  The vmcore shows there are over 14M negative dentry objects on
lru, but tracing result shows they were even not scanned at all.

Further investigation shows the memcg's vfs shrinker_map bit is not set.
So the reclaimer or dropping cache just skip calling vfs shrinker.  So
we have to reboot the hosts to get the memory back.

I didn't manage to come up with a reproducer in test environment, and
the problem can't be reproduced after rebooting.  But it seems there is
race between shrinker map bit clear and reparenting by code inspection.
The hypothesis is elaborated as below.

The memcg hierarchy on our production environment looks like:

                root
               /    \
          system   user

The main workloads are running under user slice's children, and it
creates and removes memcg frequently.  So reparenting happens very often
under user slice, but no task is under user slice directly.

So with the frequent reparenting and tight memory pressure, the below
hypothetical race condition may happen:

       CPU A                            CPU B
reparent
    dst->nr_items == 0
                                 shrinker:
                                     total_objects == 0
    add src->nr_items to dst
    set_bit
                                     return SHRINK_EMPTY
                                     clear_bit
child memcg offline
    replace child's kmemcg_id with
    parent's (in memcg_offline_kmem())
                                  list_lru_del() between shrinker runs
                                     see parent's kmemcg_id
                                     dec dst->nr_items
reparent again
    dst->nr_items may go negative
    due to concurrent list_lru_del()

                                 The second run of shrinker:
                                     read nr_items without any
                                     synchronization, so it may
                                     see intermediate negative
                                     nr_items then total_objects
                                     may return 0 coincidently

                                     keep the bit cleared
    dst->nr_items != 0
    skip set_bit
    add scr->nr_item to dst

After this point dst->nr_item may never go zero, so reparenting will not
set shrinker_map bit anymore.  And since there is no task under user
slice directly, so no new object will be added to its lru to set the
shrinker map bit either.  That bit is kept cleared forever.

How does list_lru_del() race with reparenting? It is because reparenting
replaces children's kmemcg_id to parent's without protecting from
nlru->lock, so list_lru_del() may see parent's kmemcg_id but actually
deleting items from child's lru, but dec'ing parent's nr_items, so the
parent's nr_items may go negative as commit 2788cf0c40 ("memcg:
reparent list_lrus and free kmemcg_id on css offline") says.

Since it is impossible that dst->nr_items goes negative and
src->nr_items goes zero at the same time, so it seems we could set the
shrinker map bit iff src->nr_items != 0.  We could synchronize
list_lru_count_one() and reparenting with nlru->lock, but it seems
checking src->nr_items in reparenting is the simplest and avoids lock
contention.

Fixes: fae91d6d8b ("mm/list_lru.c: set bit in memcg shrinker bitmap on first list_lru item appearance")
Suggested-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: <stable@vger.kernel.org>	[4.19]
Link: https://lkml.kernel.org/r/20201202171749.264354-1-shy828301@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-06 10:19:07 -08:00

650 lines
14 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (c) 2013 Red Hat, Inc. and Parallels Inc. All rights reserved.
* Authors: David Chinner and Glauber Costa
*
* Generic LRU infrastructure
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/list_lru.h>
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/memcontrol.h>
#include "slab.h"
#ifdef CONFIG_MEMCG_KMEM
static LIST_HEAD(list_lrus);
static DEFINE_MUTEX(list_lrus_mutex);
static void list_lru_register(struct list_lru *lru)
{
mutex_lock(&list_lrus_mutex);
list_add(&lru->list, &list_lrus);
mutex_unlock(&list_lrus_mutex);
}
static void list_lru_unregister(struct list_lru *lru)
{
mutex_lock(&list_lrus_mutex);
list_del(&lru->list);
mutex_unlock(&list_lrus_mutex);
}
static int lru_shrinker_id(struct list_lru *lru)
{
return lru->shrinker_id;
}
static inline bool list_lru_memcg_aware(struct list_lru *lru)
{
return lru->memcg_aware;
}
static inline struct list_lru_one *
list_lru_from_memcg_idx(struct list_lru_node *nlru, int idx)
{
struct list_lru_memcg *memcg_lrus;
/*
* Either lock or RCU protects the array of per cgroup lists
* from relocation (see memcg_update_list_lru_node).
*/
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;
}
static inline struct list_lru_one *
list_lru_from_kmem(struct list_lru_node *nlru, void *ptr,
struct mem_cgroup **memcg_ptr)
{
struct list_lru_one *l = &nlru->lru;
struct mem_cgroup *memcg = NULL;
if (!nlru->memcg_lrus)
goto out;
memcg = mem_cgroup_from_obj(ptr);
if (!memcg)
goto out;
l = list_lru_from_memcg_idx(nlru, memcg_cache_id(memcg));
out:
if (memcg_ptr)
*memcg_ptr = memcg;
return l;
}
#else
static void list_lru_register(struct list_lru *lru)
{
}
static void list_lru_unregister(struct list_lru *lru)
{
}
static int lru_shrinker_id(struct list_lru *lru)
{
return -1;
}
static inline bool list_lru_memcg_aware(struct list_lru *lru)
{
return false;
}
static inline struct list_lru_one *
list_lru_from_memcg_idx(struct list_lru_node *nlru, int idx)
{
return &nlru->lru;
}
static inline struct list_lru_one *
list_lru_from_kmem(struct list_lru_node *nlru, void *ptr,
struct mem_cgroup **memcg_ptr)
{
if (memcg_ptr)
*memcg_ptr = NULL;
return &nlru->lru;
}
#endif /* CONFIG_MEMCG_KMEM */
bool list_lru_add(struct list_lru *lru, struct list_head *item)
{
int nid = page_to_nid(virt_to_page(item));
struct list_lru_node *nlru = &lru->node[nid];
struct mem_cgroup *memcg;
struct list_lru_one *l;
spin_lock(&nlru->lock);
if (list_empty(item)) {
l = list_lru_from_kmem(nlru, item, &memcg);
list_add_tail(item, &l->list);
/* Set shrinker bit if the first element was added */
if (!l->nr_items++)
memcg_set_shrinker_bit(memcg, nid,
lru_shrinker_id(lru));
nlru->nr_items++;
spin_unlock(&nlru->lock);
return true;
}
spin_unlock(&nlru->lock);
return false;
}
EXPORT_SYMBOL_GPL(list_lru_add);
bool list_lru_del(struct list_lru *lru, struct list_head *item)
{
int nid = page_to_nid(virt_to_page(item));
struct list_lru_node *nlru = &lru->node[nid];
struct list_lru_one *l;
spin_lock(&nlru->lock);
if (!list_empty(item)) {
l = list_lru_from_kmem(nlru, item, NULL);
list_del_init(item);
l->nr_items--;
nlru->nr_items--;
spin_unlock(&nlru->lock);
return true;
}
spin_unlock(&nlru->lock);
return false;
}
EXPORT_SYMBOL_GPL(list_lru_del);
void list_lru_isolate(struct list_lru_one *list, struct list_head *item)
{
list_del_init(item);
list->nr_items--;
}
EXPORT_SYMBOL_GPL(list_lru_isolate);
void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item,
struct list_head *head)
{
list_move(item, head);
list->nr_items--;
}
EXPORT_SYMBOL_GPL(list_lru_isolate_move);
unsigned long list_lru_count_one(struct list_lru *lru,
int nid, struct mem_cgroup *memcg)
{
struct list_lru_node *nlru = &lru->node[nid];
struct list_lru_one *l;
unsigned long count;
rcu_read_lock();
l = list_lru_from_memcg_idx(nlru, memcg_cache_id(memcg));
count = READ_ONCE(l->nr_items);
rcu_read_unlock();
return count;
}
EXPORT_SYMBOL_GPL(list_lru_count_one);
unsigned long list_lru_count_node(struct list_lru *lru, int nid)
{
struct list_lru_node *nlru;
nlru = &lru->node[nid];
return nlru->nr_items;
}
EXPORT_SYMBOL_GPL(list_lru_count_node);
static unsigned long
__list_lru_walk_one(struct list_lru_node *nlru, int memcg_idx,
list_lru_walk_cb isolate, void *cb_arg,
unsigned long *nr_to_walk)
{
struct list_lru_one *l;
struct list_head *item, *n;
unsigned long isolated = 0;
l = list_lru_from_memcg_idx(nlru, memcg_idx);
restart:
list_for_each_safe(item, n, &l->list) {
enum lru_status ret;
/*
* decrement nr_to_walk first so that we don't livelock if we
* get stuck on large numbers of LRU_RETRY items
*/
if (!*nr_to_walk)
break;
--*nr_to_walk;
ret = isolate(item, l, &nlru->lock, cb_arg);
switch (ret) {
case LRU_REMOVED_RETRY:
assert_spin_locked(&nlru->lock);
fallthrough;
case LRU_REMOVED:
isolated++;
nlru->nr_items--;
/*
* If the lru lock has been dropped, our list
* traversal is now invalid and so we have to
* restart from scratch.
*/
if (ret == LRU_REMOVED_RETRY)
goto restart;
break;
case LRU_ROTATE:
list_move_tail(item, &l->list);
break;
case LRU_SKIP:
break;
case LRU_RETRY:
/*
* The lru lock has been dropped, our list traversal is
* now invalid and so we have to restart from scratch.
*/
assert_spin_locked(&nlru->lock);
goto restart;
default:
BUG();
}
}
return isolated;
}
unsigned long
list_lru_walk_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
list_lru_walk_cb isolate, void *cb_arg,
unsigned long *nr_to_walk)
{
struct list_lru_node *nlru = &lru->node[nid];
unsigned long ret;
spin_lock(&nlru->lock);
ret = __list_lru_walk_one(nlru, memcg_cache_id(memcg), isolate, cb_arg,
nr_to_walk);
spin_unlock(&nlru->lock);
return ret;
}
EXPORT_SYMBOL_GPL(list_lru_walk_one);
unsigned long
list_lru_walk_one_irq(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
list_lru_walk_cb isolate, void *cb_arg,
unsigned long *nr_to_walk)
{
struct list_lru_node *nlru = &lru->node[nid];
unsigned long ret;
spin_lock_irq(&nlru->lock);
ret = __list_lru_walk_one(nlru, memcg_cache_id(memcg), isolate, cb_arg,
nr_to_walk);
spin_unlock_irq(&nlru->lock);
return ret;
}
unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
list_lru_walk_cb isolate, void *cb_arg,
unsigned long *nr_to_walk)
{
long isolated = 0;
int memcg_idx;
isolated += list_lru_walk_one(lru, nid, NULL, isolate, cb_arg,
nr_to_walk);
if (*nr_to_walk > 0 && list_lru_memcg_aware(lru)) {
for_each_memcg_cache_index(memcg_idx) {
struct list_lru_node *nlru = &lru->node[nid];
spin_lock(&nlru->lock);
isolated += __list_lru_walk_one(nlru, memcg_idx,
isolate, cb_arg,
nr_to_walk);
spin_unlock(&nlru->lock);
if (*nr_to_walk <= 0)
break;
}
}
return isolated;
}
EXPORT_SYMBOL_GPL(list_lru_walk_node);
static void init_one_lru(struct list_lru_one *l)
{
INIT_LIST_HEAD(&l->list);
l->nr_items = 0;
}
#ifdef CONFIG_MEMCG_KMEM
static void __memcg_destroy_list_lru_node(struct list_lru_memcg *memcg_lrus,
int begin, int end)
{
int i;
for (i = begin; i < end; i++)
kfree(memcg_lrus->lru[i]);
}
static int __memcg_init_list_lru_node(struct list_lru_memcg *memcg_lrus,
int begin, int end)
{
int i;
for (i = begin; i < end; i++) {
struct list_lru_one *l;
l = kmalloc(sizeof(struct list_lru_one), GFP_KERNEL);
if (!l)
goto fail;
init_one_lru(l);
memcg_lrus->lru[i] = l;
}
return 0;
fail:
__memcg_destroy_list_lru_node(memcg_lrus, begin, i);
return -ENOMEM;
}
static int memcg_init_list_lru_node(struct list_lru_node *nlru)
{
struct list_lru_memcg *memcg_lrus;
int size = memcg_nr_cache_ids;
memcg_lrus = kvmalloc(sizeof(*memcg_lrus) +
size * sizeof(void *), GFP_KERNEL);
if (!memcg_lrus)
return -ENOMEM;
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)
{
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_local().
*/
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_local(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,
int old_size, int new_size)
{
struct list_lru_memcg *old, *new;
BUG_ON(old_size > new_size);
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;
if (__memcg_init_list_lru_node(new, old_size, new_size)) {
kvfree(new);
return -ENOMEM;
}
memcpy(&new->lru, &old->lru, old_size * sizeof(void *));
/*
* 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);
rcu_assign_pointer(nlru->memcg_lrus, new);
spin_unlock_irq(&nlru->lock);
call_rcu(&old->rcu, kvfree_rcu_local);
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(memcg_lrus, old_size, new_size);
}
static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
{
int i;
lru->memcg_aware = memcg_aware;
if (!memcg_aware)
return 0;
for_each_node(i) {
if (memcg_init_list_lru_node(&lru->node[i]))
goto fail;
}
return 0;
fail:
for (i = i - 1; i >= 0; i--) {
if (!lru->node[i].memcg_lrus)
continue;
memcg_destroy_list_lru_node(&lru->node[i]);
}
return -ENOMEM;
}
static void memcg_destroy_list_lru(struct list_lru *lru)
{
int i;
if (!list_lru_memcg_aware(lru))
return;
for_each_node(i)
memcg_destroy_list_lru_node(&lru->node[i]);
}
static int memcg_update_list_lru(struct list_lru *lru,
int old_size, int new_size)
{
int i;
if (!list_lru_memcg_aware(lru))
return 0;
for_each_node(i) {
if (memcg_update_list_lru_node(&lru->node[i],
old_size, new_size))
goto fail;
}
return 0;
fail:
for (i = i - 1; i >= 0; i--) {
if (!lru->node[i].memcg_lrus)
continue;
memcg_cancel_update_list_lru_node(&lru->node[i],
old_size, new_size);
}
return -ENOMEM;
}
static void memcg_cancel_update_list_lru(struct list_lru *lru,
int old_size, int new_size)
{
int i;
if (!list_lru_memcg_aware(lru))
return;
for_each_node(i)
memcg_cancel_update_list_lru_node(&lru->node[i],
old_size, new_size);
}
int memcg_update_all_list_lrus(int new_size)
{
int ret = 0;
struct list_lru *lru;
int old_size = memcg_nr_cache_ids;
mutex_lock(&list_lrus_mutex);
list_for_each_entry(lru, &list_lrus, list) {
ret = memcg_update_list_lru(lru, old_size, new_size);
if (ret)
goto fail;
}
out:
mutex_unlock(&list_lrus_mutex);
return ret;
fail:
list_for_each_entry_continue_reverse(lru, &list_lrus, list)
memcg_cancel_update_list_lru(lru, old_size, new_size);
goto out;
}
static void memcg_drain_list_lru_node(struct list_lru *lru, int nid,
int src_idx, struct mem_cgroup *dst_memcg)
{
struct list_lru_node *nlru = &lru->node[nid];
int dst_idx = dst_memcg->kmemcg_id;
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);
if (src->nr_items) {
dst->nr_items += src->nr_items;
memcg_set_shrinker_bit(dst_memcg, nid, lru_shrinker_id(lru));
src->nr_items = 0;
}
spin_unlock_irq(&nlru->lock);
}
static void memcg_drain_list_lru(struct list_lru *lru,
int src_idx, struct mem_cgroup *dst_memcg)
{
int i;
if (!list_lru_memcg_aware(lru))
return;
for_each_node(i)
memcg_drain_list_lru_node(lru, i, src_idx, dst_memcg);
}
void memcg_drain_all_list_lrus(int src_idx, struct mem_cgroup *dst_memcg)
{
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_memcg);
mutex_unlock(&list_lrus_mutex);
}
#else
static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
{
return 0;
}
static void memcg_destroy_list_lru(struct list_lru *lru)
{
}
#endif /* CONFIG_MEMCG_KMEM */
int __list_lru_init(struct list_lru *lru, bool memcg_aware,
struct lock_class_key *key, struct shrinker *shrinker)
{
int i;
int err = -ENOMEM;
#ifdef CONFIG_MEMCG_KMEM
if (shrinker)
lru->shrinker_id = shrinker->id;
else
lru->shrinker_id = -1;
#endif
memcg_get_cache_ids();
lru->node = kcalloc(nr_node_ids, sizeof(*lru->node), GFP_KERNEL);
if (!lru->node)
goto out;
for_each_node(i) {
spin_lock_init(&lru->node[i].lock);
if (key)
lockdep_set_class(&lru->node[i].lock, key);
init_one_lru(&lru->node[i].lru);
}
err = memcg_init_list_lru(lru, memcg_aware);
if (err) {
kfree(lru->node);
/* Do this so a list_lru_destroy() doesn't crash: */
lru->node = NULL;
goto out;
}
list_lru_register(lru);
out:
memcg_put_cache_ids();
return err;
}
EXPORT_SYMBOL_GPL(__list_lru_init);
void list_lru_destroy(struct list_lru *lru)
{
/* Already destroyed or not yet initialized? */
if (!lru->node)
return;
memcg_get_cache_ids();
list_lru_unregister(lru);
memcg_destroy_list_lru(lru);
kfree(lru->node);
lru->node = NULL;
#ifdef CONFIG_MEMCG_KMEM
lru->shrinker_id = -1;
#endif
memcg_put_cache_ids();
}
EXPORT_SYMBOL_GPL(list_lru_destroy);