[patch 076/163] mm: memcg/slab: deprecate slab_root_caches

Andrew Morton
2020-08-07T06:21:24Z

From: Roman Gushchin <guro@fb.com>
Subject: mm: memcg/slab: deprecate slab_root_caches

Currently there are two lists of kmem_caches:
1) slab_caches, which contains all kmem_caches,
2) slab_root_caches, which contains only root kmem_caches.

And there is some preprocessor magic to have a single list if
CONFIG_MEMCG_KMEM isn't enabled.

It was required earlier because the number of non-root kmem_caches was
proportional to the number of memory cgroups and could reach really big
values. Now, when it cannot exceed the number of root kmem_caches, there
is really no reason to maintain two lists.

We never iterate over the slab_root_caches list on any hot paths, so it's
perfectly fine to iterate over slab_caches and filter out non-root
kmem_caches.

It allows to remove a lot of config-dependent code and two pointers from
the kmem_cache structure.

Link: http://lkml.kernel.org/r/20200623174037.3951353-16-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/slab.c | 1 -
mm/slab.h | 17 -----------------
mm/slab_common.c | 37 ++++++++-----------------------------
mm/slub.c | 1 -
4 files changed, 8 insertions(+), 48 deletions(-)

--- a/mm/slab.c~mm-memcg-slab-deprecate-slab_root_caches
+++ a/mm/slab.c
@@ -1249,7 +1249,6 @@ void __init kmem_cache_init(void)
nr_node_ids * sizeof(struct kmem_cache_node *),
SLAB_HWCACHE_ALIGN, 0, 0);
list_add(&kmem_cache->list, &slab_caches);
- memcg_link_cache(kmem_cache);
slab_state = PARTIAL;

/*
--- a/mm/slab_common.c~mm-memcg-slab-deprecate-slab_root_caches
+++ a/mm/slab_common.c
@@ -131,9 +131,6 @@ int __kmem_cache_alloc_bulk(struct kmem_
}

#ifdef CONFIG_MEMCG_KMEM
-
-LIST_HEAD(slab_root_caches);
-
static void memcg_kmem_cache_create_func(struct work_struct *work)
{
struct kmem_cache *cachep = container_of(work, struct kmem_cache,
@@ -156,27 +153,11 @@ static void init_memcg_params(struct kme
else
slab_init_memcg_params(s);
}
-
-void memcg_link_cache(struct kmem_cache *s)
-{
- if (is_root_cache(s))
- list_add(&s->root_caches_node, &slab_root_caches);
-}
-
-static void memcg_unlink_cache(struct kmem_cache *s)
-{
- if (is_root_cache(s))
- list_del(&s->root_caches_node);
-}
#else
static inline void init_memcg_params(struct kmem_cache *s,
struct kmem_cache *root_cache)
{
}
-
-static inline void memcg_unlink_cache(struct kmem_cache *s)
-{
-}
#endif /* CONFIG_MEMCG_KMEM */

/*
@@ -253,7 +234,7 @@ struct kmem_cache *find_mergeable(unsign
if (flags & SLAB_NEVER_MERGE)
return NULL;

- list_for_each_entry_reverse(s, &slab_root_caches, root_caches_node) {
+ list_for_each_entry_reverse(s, &slab_caches, list) {
if (slab_unmergeable(s))
continue;

@@ -312,7 +293,6 @@ static struct kmem_cache *create_cache(c

s->refcount = 1;
list_add(&s->list, &slab_caches);
- memcg_link_cache(s);
out:
if (err)
return ERR_PTR(err);
@@ -507,7 +487,6 @@ static int shutdown_cache(struct kmem_ca
if (__kmem_cache_shutdown(s) != 0)
return -EBUSY;

- memcg_unlink_cache(s);
list_del(&s->list);

if (s->flags & SLAB_TYPESAFE_BY_RCU) {
@@ -751,7 +730,6 @@ struct kmem_cache *__init create_kmalloc

create_boot_cache(s, name, size, flags, useroffset, usersize);
list_add(&s->list, &slab_caches);
- memcg_link_cache(s);
s->refcount = 1;
return s;
}
@@ -1107,12 +1085,12 @@ static void print_slabinfo_header(struct
void *slab_start(struct seq_file *m, loff_t *pos)
{
mutex_lock(&slab_mutex);
- return seq_list_start(&slab_root_caches, *pos);
+ return seq_list_start(&slab_caches, *pos);
}

void *slab_next(struct seq_file *m, void *p, loff_t *pos)
{
- return seq_list_next(p, &slab_root_caches, pos);
+ return seq_list_next(p, &slab_caches, pos);
}

void slab_stop(struct seq_file *m, void *p)
@@ -1165,11 +1143,12 @@ static void cache_show(struct kmem_cache

static int slab_show(struct seq_file *m, void *p)
{
- struct kmem_cache *s = list_entry(p, struct kmem_cache, root_caches_node);
+ struct kmem_cache *s = list_entry(p, struct kmem_cache, list);

- if (p == slab_root_caches.next)
+ if (p == slab_caches.next)
print_slabinfo_header(m);
- cache_show(s, m);
+ if (is_root_cache(s))
+ cache_show(s, m);
return 0;
}

@@ -1271,7 +1250,7 @@ static int memcg_slabinfo_show(struct se
mutex_lock(&slab_mutex);
seq_puts(m, "# <name> <css_id[:dead|deact]> <active_objs> <num_objs>");
seq_puts(m, " <active_slabs> <num_slabs>\n");
- list_for_each_entry(s, &slab_root_caches, root_caches_node) {
+ list_for_each_entry(s, &slab_caches, list) {
/*
* Skip kmem caches that don't have the memcg cache.
*/
--- a/mm/slab.h~mm-memcg-slab-deprecate-slab_root_caches
+++ a/mm/slab.h
@@ -44,14 +44,12 @@ struct kmem_cache {
*
* @memcg_cache: pointer to memcg kmem cache, used by all non-root memory
* cgroups.
- * @root_caches_node: list node for slab_root_caches list.
* @work: work struct used to create the non-root cache.
*/
struct memcg_cache_params {
struct kmem_cache *root_cache;

struct kmem_cache *memcg_cache;
- struct list_head __root_caches_node;
struct work_struct work;
};
#endif /* CONFIG_SLOB */
@@ -265,11 +263,6 @@ static inline bool kmem_cache_debug_flag
}

#ifdef CONFIG_MEMCG_KMEM
-
-/* List of all root caches. */
-extern struct list_head slab_root_caches;
-#define root_caches_node memcg_params.__root_caches_node
-
static inline bool is_root_cache(struct kmem_cache *s)
{
return !s->memcg_params.root_cache;
@@ -447,14 +440,8 @@ static inline void memcg_slab_free_hook(
}

extern void slab_init_memcg_params(struct kmem_cache *);
-extern void memcg_link_cache(struct kmem_cache *s);

#else /* CONFIG_MEMCG_KMEM */
-
-/* If !memcg, all caches are root. */
-#define slab_root_caches slab_caches
-#define root_caches_node list
-
static inline bool is_root_cache(struct kmem_cache *s)
{
return true;
@@ -523,10 +510,6 @@ static inline void slab_init_memcg_param
{
}

-static inline void memcg_link_cache(struct kmem_cache *s)
-{
-}
-
#endif /* CONFIG_MEMCG_KMEM */

static inline struct kmem_cache *virt_to_cache(const void *obj)
--- a/mm/slub.c~mm-memcg-slab-deprecate-slab_root_caches
+++ a/mm/slub.c
@@ -4360,7 +4360,6 @@ static struct kmem_cache * __init bootst
}
slab_init_memcg_params(s);
list_add(&s->list, &slab_caches);
- memcg_link_cache(s);
return s;
}

_