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Commit 6164281a authored by Pavel Emelyanov's avatar Pavel Emelyanov Committed by Linus Torvalds
Browse files

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: default avatarPavel Emelyanov <xemul@openvz.org>
Acked-by: default avatarSerge E. Hallyn <serge@hallyn.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e020e742

include/linux/user_namespace.h

+1 −1
Original line number Original line Diff line number Diff line
@@ -6,7 +6,7 @@ 
#include <linux/sched.h>

#include <linux/sched.h>

#include <linux/err.h>

#include <linux/err.h>





#define UIDHASH_BITS	(CONFIG_BASE_SMALL ? 3 : 8)

#define UIDHASH_BITS	(CONFIG_BASE_SMALL ? 3 : 7)

#define UIDHASH_SZ	(1 << UIDHASH_BITS)

#define UIDHASH_SZ	(1 << UIDHASH_BITS)





struct user_namespace {

struct user_namespace {

kernel/user_namespace.c

+12 −3
Original line number Original line Diff line number Diff line
@@ -12,6 +12,8 @@ 
#include <linux/highuid.h>

#include <linux/highuid.h>

#include <linux/cred.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

 * 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

 * 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;

	struct user_struct *root_user;

	int n;

	int n;





	ns = kmalloc(sizeof(struct user_namespace), GFP_KERNEL);

	ns = kmem_cache_alloc(user_ns_cachep, GFP_KERNEL);

	if (!ns)

	if (!ns)

		return -ENOMEM;

		return -ENOMEM;
@@ -38,7 +40,7 @@ int create_user_ns(struct cred *new) 
	/* Alloc new root user.  */

	/* Alloc new root user.  */

	root_user = alloc_uid(ns, 0);

	root_user = alloc_uid(ns, 0);

	if (!root_user) {

	if (!root_user) {

		kfree(ns);

		kmem_cache_free(user_ns_cachep, ns);

		return -ENOMEM;

		return -ENOMEM;

	}

	}
@@ -71,7 +73,7 @@ static void free_user_ns_work(struct work_struct *work) 
	struct user_namespace *ns =

	struct user_namespace *ns =

		container_of(work, struct user_namespace, destroyer);

		container_of(work, struct user_namespace, destroyer);

	free_uid(ns->creator);

	free_uid(ns->creator);

	kfree(ns);

	kmem_cache_free(user_ns_cachep, ns);

}

}





void free_user_ns(struct kref *kref)

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 */

	/* No useful relationship so no mapping */

	return overflowgid;

	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);