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.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
---
Documentation/kernel-parameters.txt | 8 ++++++++
init/Kconfig | 14 ++++++++++++++
mm/slub.c | 29 ++++++++++++++++++++++++++---
3 files changed, 48 insertions(+), 3 deletions(-)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3517,6 +3517,14 @@ bytes respectively. Such letter suffixes
last alloc / free. For more information see
Documentation/vm/slub.txt.
+ slub_memcg_sysfs= [MM, SLUB]
+ Determines whether to enable sysfs directories for
+ memory cgroup sub-caches. 1 to enable, 0 to disable.
+ The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
+ Enabling this can lead to a very high number of debug
+ directories and files being created under
+ /sys/kernel/slub.
+
slub_max_order= [MM, SLUB]
Determines the maximum allowed order for slabs.
A high setting may cause OOMs due to memory
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1786,6 +1786,20 @@ config SLUB_DEBUG
SLUB sysfs support. /sys/slab will not exist and there will be
no support for cache validation etc.
+config SLUB_MEMCG_SYSFS_ON
+ default n
+ bool "Enable memcg SLUB sysfs support by default" if EXPERT
+ depends on SLUB && SYSFS && MEMCG
+ help
+ SLUB creates a directory under /sys/kernel/slab for each
+ allocation cache to host info and debug files. If memory
+ cgroup is enabled, each cache can have per memory cgroup
+ caches. SLUB can create the same sysfs directories for these
+ caches under /sys/kernel/slab/CACHE/cgroup but it can lead
+ to a very high number of debug files being created. This is
+ controlled by slub_memcg_sysfs boot parameter and this
+ config option determines the parameter's default value.
+
config COMPAT_BRK
bool "Disable heap randomization"
default y
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4700,6 +4700,22 @@ 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)
{
@@ -5603,8 +5619,14 @@ static int sysfs_slab_add(struct kmem_ca
{
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.
@@ -5621,7 +5643,7 @@ static int sysfs_slab_add(struct kmem_ca
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;
@@ -5631,7 +5653,7 @@ static int sysfs_slab_add(struct kmem_ca
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;
@@ -5673,7 +5695,8 @@ static void sysfs_slab_remove(struct kme
return;
#ifdef CONFIG_MEMCG
- kset_unregister(s->memcg_kset);
+ if (s->memcg_kset)
+ kset_unregister(s->memcg_kset);
#endif
kobject_uevent(&s->kobj, KOBJ_REMOVE);
kobject_del(&s->kobj);
--
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