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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>
This commit is contained in:
Pavel Emelyanov 2011-01-12 17:00:46 -08:00 committed by Linus Torvalds
parent e020e742e5
commit 6164281ab7
2 changed files with 13 additions and 4 deletions
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2
include/linux/user_namespace.h
View File

@ -6,7 +6,7 @@
#include <linux/sched.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)
struct user_namespace {

15
kernel/user_namespace.c
View File

@ -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);