mm, slub: remove slub_memcg_sysfs boot param and CONFIG_SLUB_MEMCG_SYSFS_ON

The boot param and config determine the value of memcg_sysfs_enabled,
which is unused since commit 10befea9 ("mm: memcg/slab: use a single
set of kmem_caches for all allocations") as there are no per-memcg kmem
caches anymore.

Link: https://lkml.kernel.org/r/20210127124745.7928-1-vbabka@suse.czSigned-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: David Rientjes <rientjes@google.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/admin-guide/kernel-parameters.txt

@@ -4899,14 +4899,6 @@
 			last alloc / free. For more information see
 			Documentation/vm/slub.rst.
 
-	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

init/Kconfig

@@ -1861,20 +1861,6 @@ 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

mm/slub.c

@@ -4943,22 +4943,6 @@ 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)
 {