user_ns: improve the user_ns on-the-slab packaging

Currently on 64-bit arch the user_namespace is 2096 and when being
kmalloc-ed it resides on a 4k slab wasting 2003 bytes.

If we allocate a separate cache for it and reduce the hash size from 128
to 64 chains the packaging becomes *much* better - the struct is 1072
bytes and the hole between is 98 bytes.

[akpm@linux-foundation.org: s/__initcall/module_init/]
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Serge E. Hallyn <serge@hallyn.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 3 deletions

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 25915832291a..9da289c34f22 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -12,6 +12,8 @@
 #include <linux/highuid.h>
 #include <linux/cred.h>
 
+static struct kmem_cache *user_ns_cachep __read_mostly;
+
 /*
  * Create a new user namespace, deriving the creator from the user in the
  * passed credentials, and replacing that user with the new root user for the
@@ -26,7 +28,7 @@ int create_user_ns(struct cred *new)
         struct user_struct *root_user;
         int n;
 
-        ns = kmalloc(sizeof(struct user_namespace), GFP_KERNEL);
+        ns = kmem_cache_alloc(user_ns_cachep, GFP_KERNEL);
         if (!ns)
                 return -ENOMEM;
 
@@ -38,7 +40,7 @@ int create_user_ns(struct cred *new)
         /* Alloc new root user.  */
         root_user = alloc_uid(ns, 0);
         if (!root_user) {
-                kfree(ns);
+                kmem_cache_free(user_ns_cachep, ns);
                 return -ENOMEM;
         }
 
@@ -71,7 +73,7 @@ static void free_user_ns_work(struct work_struct *work)
         struct user_namespace *ns =
                 container_of(work, struct user_namespace, destroyer);
         free_uid(ns->creator);
-        kfree(ns);
+        kmem_cache_free(user_ns_cachep, ns);
 }
 
 void free_user_ns(struct kref *kref)
@@ -126,3 +128,10 @@ gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t
         /* No useful relationship so no mapping */
         return overflowgid;
 }
+
+static __init int user_namespaces_init(void)
+{
+        user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
+        return 0;
+}
+module_init(user_namespaces_init);