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slub: make sysfs directories for memcg sub-caches optional

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SLUB creates a per-cache directory under /sys/kernel/slab which hosts a
bunch of debug files.  Usually, there aren't that many caches on a
system and this doesn't really matter; however, if memcg is in use, each
cache can have per-cgroup sub-caches.  SLUB creates the same directories
for these sub-caches under /sys/kernel/slab/$CACHE/cgroup.

Unfortunately, because there can be a lot of cgroups, active or
draining, the product of the numbers of caches, cgroups and files in
each directory can reach a very high number - hundreds of thousands is
commonplace.  Millions and beyond aren't difficult to reach either.

What's under /sys/kernel/slab is primarily for debugging and the
information and control on the a root cache already cover its
sub-caches.  While having a separate directory for each sub-cache can be
helpful for development, it doesn't make much sense to pay this amount
of overhead by default.

This patch introduces a boot parameter slub_memcg_sysfs which determines
whether to create sysfs directories for per-memcg sub-caches.  It also
adds CONFIG_SLUB_MEMCG_SYSFS_ON which determines the boot parameter's
default value and defaults to 0.

[akpm@linux-foundation.org: kset_unregister(NULL) is legal]
Link: http://lkml.kernel.org/r/20170204145203.GB26958@mtj.duckdns.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Tejun Heo
2017-02-22 15:41:39 -08:00
committed by Linus Torvalds
parent 17cc4dfeda
commit 1663f26df3
3 changed files with 46 additions and 2 deletions
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26
mm/slub.c
View File

@@ -4708,6 +4708,22 @@ enum slab_stat_type {
#define SO_OBJECTS (1 << SL_OBJECTS)
#define SO_TOTAL (1 << SL_TOTAL)
#ifdef CONFIG_MEMCG
static bool memcg_sysfs_enabled = IS_ENABLED(CONFIG_SLUB_MEMCG_SYSFS_ON);
static int __init setup_slub_memcg_sysfs(char *str)
{
int v;
if (get_option(&str, &v) > 0)
memcg_sysfs_enabled = v;
return 1;
}
__setup("slub_memcg_sysfs=", setup_slub_memcg_sysfs);
#endif
static ssize_t show_slab_objects(struct kmem_cache *s,
char *buf, unsigned long flags)
{
@@ -5611,8 +5627,14 @@ static int sysfs_slab_add(struct kmem_cache *s)
{
int err;
const char *name;
struct kset *kset = cache_kset(s);
int unmergeable = slab_unmergeable(s);
if (!kset) {
kobject_init(&s->kobj, &slab_ktype);
return 0;
}
if (unmergeable) {
/*
* Slabcache can never be merged so we can use the name proper.
@@ -5629,7 +5651,7 @@ static int sysfs_slab_add(struct kmem_cache *s)
name = create_unique_id(s);
}
s->kobj.kset = cache_kset(s);
s->kobj.kset = kset;
err = kobject_init_and_add(&s->kobj, &slab_ktype, NULL, "%s", name);
if (err)
goto out;
@@ -5639,7 +5661,7 @@ static int sysfs_slab_add(struct kmem_cache *s)
goto out_del_kobj;
#ifdef CONFIG_MEMCG
if (is_root_cache(s)) {
if (is_root_cache(s) && memcg_sysfs_enabled) {
s->memcg_kset = kset_create_and_add("cgroup", NULL, &s->kobj);
if (!s->memcg_kset) {
err = -ENOMEM;