mm: list_lru: allocate list_lru_one only when needed

In our server, we found a suspected memory leak problem.  The kmalloc-32
consumes more than 6GB of memory.  Other kmem_caches consume less than
2GB memory.

After our in-depth analysis, the memory consumption of kmalloc-32 slab
cache is the cause of list_lru_one allocation.

  crash> p memcg_nr_cache_ids
  memcg_nr_cache_ids = $2 = 24574

memcg_nr_cache_ids is very large and memory consumption of each list_lru
can be calculated with the following formula.

  num_numa_node * memcg_nr_cache_ids * 32 (kmalloc-32)

There are 4 numa nodes in our system, so each list_lru consumes ~3MB.

  crash> list super_blocks | wc -l
  952

Every mount will register 2 list lrus, one is for inode, another is for
dentry.  There are 952 super_blocks.  So the total memory is 952 * 2 * 3
MB (~5.6GB).  But the number of memory cgroup is less than 500.  So I
guess more than 12286 containers have been deployed on this machine (I do
not know why there are so many containers, it may be a user's bug or the
user really want to do that).  And memcg_nr_cache_ids has not been reduced
to a suitable value.  This can waste a lot of memory.

Now the infrastructure for dynamic list_lru_one allocation is ready, so
remove statically allocated memory code to save memory.

Link: https://lkml.kernel.org/r/20220228122126.37293-11-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Anna Schumaker <Anna.Schumaker@Netapp.com>
Cc: Chao Yu <chao@kernel.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Fam Zheng <fam.zheng@bytedance.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kari Argillander <kari.argillander@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index ab912c4..c36db6d 100644 (file)
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -32,14 +32,15 @@ struct list_lru_one {
 };
 
 struct list_lru_per_memcg {
+       struct rcu_head         rcu;
        /* array of per cgroup per node lists, indexed by node id */
-       struct list_lru_one     node[0];
+       struct list_lru_one     node[];
 };
 
 struct list_lru_memcg {
        struct rcu_head                 rcu;
        /* array of per cgroup lists, indexed by memcg_cache_id */
-       struct list_lru_per_memcg       *mlru[];
+       struct list_lru_per_memcg __rcu *mlru[];
 };
 
 struct list_lru_node {
@@ -77,7 +78,7 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
 int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
                         gfp_t gfp);
 int memcg_update_all_list_lrus(int num_memcgs);
-void memcg_drain_all_list_lrus(int src_idx, struct mem_cgroup *dst_memcg);
+void memcg_drain_all_list_lrus(struct mem_cgroup *src, struct mem_cgroup *dst);
 
 /**
  * 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 bffa805..fc938d8 100644 (file)
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -60,8 +60,12 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
         * from relocation (see memcg_update_list_lru).
         */
        mlrus = rcu_dereference_check(lru->mlrus, lockdep_is_held(&nlru->lock));
-       if (mlrus && idx >= 0)
-               return &mlrus->mlru[idx]->node[nid];
+       if (mlrus && idx >= 0) {
+               struct list_lru_per_memcg *mlru;
+
+               mlru = rcu_dereference_check(mlrus->mlru[idx], true);
+               return mlru ? &mlru->node[nid] : NULL;
+       }
        return &nlru->lru;
 }
 
@@ -188,7 +192,7 @@ unsigned long list_lru_count_one(struct list_lru *lru,
 
        rcu_read_lock();
        l = list_lru_from_memcg_idx(lru, nid, memcg_cache_id(memcg));
-       count = READ_ONCE(l->nr_items);
+       count = l ? READ_ONCE(l->nr_items) : 0;
        rcu_read_unlock();
 
        if (unlikely(count < 0))
@@ -217,8 +221,11 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx,
        struct list_head *item, *n;
        unsigned long isolated = 0;
 
-       l = list_lru_from_memcg_idx(lru, nid, memcg_idx);
 restart:
+       l = list_lru_from_memcg_idx(lru, nid, memcg_idx);
+       if (!l)
+               goto out;
+
        list_for_each_safe(item, n, &l->list) {
                enum lru_status ret;
 
@@ -262,6 +269,7 @@ restart:
                        BUG();
                }
        }
+out:
        return isolated;
 }
 
@@ -354,20 +362,25 @@ static struct list_lru_per_memcg *memcg_init_list_lru_one(gfp_t gfp)
        return mlru;
 }
 
-static int memcg_init_list_lru_range(struct list_lru_memcg *mlrus,
-                                    int begin, int end)
+static void memcg_list_lru_free(struct list_lru *lru, int src_idx)
 {
-       int i;
+       struct list_lru_memcg *mlrus;
+       struct list_lru_per_memcg *mlru;
 
-       for (i = begin; i < end; i++) {
-               mlrus->mlru[i] = memcg_init_list_lru_one(GFP_KERNEL);
-               if (!mlrus->mlru[i])
-                       goto fail;
-       }
-       return 0;
-fail:
-       memcg_destroy_list_lru_range(mlrus, begin, i);
-       return -ENOMEM;
+       spin_lock_irq(&lru->lock);
+       mlrus = rcu_dereference_protected(lru->mlrus, true);
+       mlru = rcu_dereference_protected(mlrus->mlru[src_idx], true);
+       rcu_assign_pointer(mlrus->mlru[src_idx], NULL);
+       spin_unlock_irq(&lru->lock);
+
+       /*
+        * The __list_lru_walk_one() can walk the list of this node.
+        * We need kvfree_rcu() here. And the walking of the list
+        * is under lru->node[nid]->lock, which can serve as a RCU
+        * read-side critical section.
+        */
+       if (mlru)
+               kvfree_rcu(mlru, rcu);
 }
 
 static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
@@ -381,14 +394,10 @@ static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
 
        spin_lock_init(&lru->lock);
 
-       mlrus = kvmalloc(struct_size(mlrus, mlru, size), GFP_KERNEL);
+       mlrus = kvzalloc(struct_size(mlrus, mlru, size), GFP_KERNEL);
        if (!mlrus)
                return -ENOMEM;
 
-       if (memcg_init_list_lru_range(mlrus, 0, size)) {
-               kvfree(mlrus);
-               return -ENOMEM;
-       }
        RCU_INIT_POINTER(lru->mlrus, mlrus);
 
        return 0;
@@ -422,13 +431,9 @@ static int memcg_update_list_lru(struct list_lru *lru, int old_size, int new_siz
        if (!new)
                return -ENOMEM;
 
-       if (memcg_init_list_lru_range(new, old_size, new_size)) {
-               kvfree(new);
-               return -ENOMEM;
-       }
-
        spin_lock_irq(&lru->lock);
        memcpy(&new->mlru, &old->mlru, flex_array_size(new, mlru, old_size));
+       memset(&new->mlru[old_size], 0, flex_array_size(new, mlru, new_size - old_size));
        rcu_assign_pointer(lru->mlrus, new);
        spin_unlock_irq(&lru->lock);
 
@@ -436,20 +441,6 @@ static int memcg_update_list_lru(struct list_lru *lru, int old_size, int new_siz
        return 0;
 }
 
-static void memcg_cancel_update_list_lru(struct list_lru *lru,
-                                        int old_size, int new_size)
-{
-       struct list_lru_memcg *mlrus;
-
-       mlrus = rcu_dereference_protected(lru->mlrus,
-                                         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_range(mlrus, old_size, new_size);
-}
-
 int memcg_update_all_list_lrus(int new_size)
 {
        int ret = 0;
@@ -460,15 +451,10 @@ int memcg_update_all_list_lrus(int new_size)
        list_for_each_entry(lru, &memcg_list_lrus, list) {
                ret = memcg_update_list_lru(lru, old_size, new_size);
                if (ret)
-                       goto fail;
+                       break;
        }
-out:
        mutex_unlock(&list_lrus_mutex);
        return ret;
-fail:
-       list_for_each_entry_continue_reverse(lru, &memcg_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,
@@ -485,6 +471,8 @@ static void memcg_drain_list_lru_node(struct list_lru *lru, int nid,
        spin_lock_irq(&nlru->lock);
 
        src = list_lru_from_memcg_idx(lru, nid, src_idx);
+       if (!src)
+               goto out;
        dst = list_lru_from_memcg_idx(lru, nid, dst_idx);
 
        list_splice_init(&src->list, &dst->list);
@@ -494,7 +482,7 @@ static void memcg_drain_list_lru_node(struct list_lru *lru, int nid,
                set_shrinker_bit(dst_memcg, nid, lru_shrinker_id(lru));
                src->nr_items = 0;
        }
-
+out:
        spin_unlock_irq(&nlru->lock);
 }
 
@@ -505,15 +493,41 @@ static void memcg_drain_list_lru(struct list_lru *lru,
 
        for_each_node(i)
                memcg_drain_list_lru_node(lru, i, src_idx, dst_memcg);
+
+       memcg_list_lru_free(lru, src_idx);
 }
 
-void memcg_drain_all_list_lrus(int src_idx, struct mem_cgroup *dst_memcg)
+void memcg_drain_all_list_lrus(struct mem_cgroup *src, struct mem_cgroup *dst)
 {
+       struct cgroup_subsys_state *css;
        struct list_lru *lru;
+       int src_idx = src->kmemcg_id;
+
+       /*
+        * 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. So we can safely free this cgroup's
+        * list lrus in memcg_list_lru_free().
+        *
+        * Changing ->kmemcg_id to the parent can prevent memcg_list_lru_alloc()
+        * from allocating list lrus for this cgroup after memcg_list_lru_free()
+        * call.
+        */
+       rcu_read_lock();
+       css_for_each_descendant_pre(css, &src->css) {
+               struct mem_cgroup *memcg;
+
+               memcg = mem_cgroup_from_css(css);
+               memcg->kmemcg_id = dst->kmemcg_id;
+       }
+       rcu_read_unlock();
 
        mutex_lock(&list_lrus_mutex);
        list_for_each_entry(lru, &memcg_list_lrus, list)
-               memcg_drain_list_lru(lru, src_idx, dst_memcg);
+               memcg_drain_list_lru(lru, src_idx, dst);
        mutex_unlock(&list_lrus_mutex);
 }
 
@@ -528,7 +542,7 @@ static bool memcg_list_lru_allocated(struct mem_cgroup *memcg,
                return true;
 
        rcu_read_lock();
-       allocated = !!rcu_dereference(lru->mlrus)->mlru[idx];
+       allocated = !!rcu_access_pointer(rcu_dereference(lru->mlrus)->mlru[idx]);
        rcu_read_unlock();
 
        return allocated;
@@ -576,11 +590,12 @@ int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
        mlrus = rcu_dereference_protected(lru->mlrus, true);
        while (i--) {
                int index = table[i].memcg->kmemcg_id;
+               struct list_lru_per_memcg *mlru = table[i].mlru;
 
-               if (mlrus->mlru[index])
-                       kfree(table[i].mlru);
+               if (index < 0 || rcu_dereference_protected(mlrus->mlru[index], true))
+                       kfree(mlru);
                else
-                       mlrus->mlru[index] = table[i].mlru;
+                       rcu_assign_pointer(mlrus->mlru[index], mlru);
        }
        spin_unlock_irqrestore(&lru->lock, flags);
 

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f08a0dc..69c09ef 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3709,6 +3709,10 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
 
        memcg_reparent_objcgs(memcg, parent);
 
+       /*
+        * memcg_drain_all_list_lrus() can change memcg->kmemcg_id.
+        * Cache it to local @kmemcg_id.
+        */
        kmemcg_id = memcg->kmemcg_id;
 
        /*
@@ -3717,7 +3721,7 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
         * The ordering is imposed by list_lru_node->lock taken by
         * memcg_drain_all_list_lrus().
         */
-       memcg_drain_all_list_lrus(kmemcg_id, parent);
+       memcg_drain_all_list_lrus(memcg, parent);
 
        memcg_free_cache_id(kmemcg_id);
 }