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authorAlexey Dobriyan <adobriyan@gmail.com>2018-03-20 21:51:06 +0300
committerEric W. Biederman <ebiederm@xmission.com>2018-03-21 09:40:17 -0500
commitdd206bec9a446884805370b1c16c1d7a97036777 (patch)
treeeaacdddc5f008401906b962ff1feb4a9cace9bfc
parent91ab883eb21325ad80f3473633f794c78ac87f51 (diff)
pidns: simpler allocation of pid_* caches
Those pid_* caches are created on demand when a process advances to the new level of pid namespace. Which means pointers are stable, write only and thus can be packed into an array instead of spreading them over and using lists(!) to find them. Both first and subsequent clone/unshare(CLONE_NEWPID) become faster. Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
-rw-r--r--kernel/pid_namespace.c67
1 files changed, 24 insertions, 43 deletions
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 0b53eef7d34b..773b2b31734f 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -23,55 +23,39 @@
#include <linux/sched/signal.h>
#include <linux/idr.h>
-struct pid_cache {
- int nr_ids;
- char name[16];
- struct kmem_cache *cachep;
- struct list_head list;
-};
-
-static LIST_HEAD(pid_caches_lh);
static DEFINE_MUTEX(pid_caches_mutex);
static struct kmem_cache *pid_ns_cachep;
+/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
+#define MAX_PID_NS_LEVEL 32
+/* Write once array, filled from the beginning. */
+static struct kmem_cache *pid_cache[MAX_PID_NS_LEVEL];
/*
* creates the kmem cache to allocate pids from.
- * @nr_ids: the number of numerical ids this pid will have to carry
+ * @level: pid namespace level
*/
-static struct kmem_cache *create_pid_cachep(int nr_ids)
+static struct kmem_cache *create_pid_cachep(unsigned int level)
{
- struct pid_cache *pcache;
- struct kmem_cache *cachep;
-
+ /* Level 0 is init_pid_ns.pid_cachep */
+ struct kmem_cache **pkc = &pid_cache[level - 1];
+ struct kmem_cache *kc;
+ char name[4 + 10 + 1];
+ unsigned int len;
+
+ kc = READ_ONCE(*pkc);
+ if (kc)
+ return kc;
+
+ snprintf(name, sizeof(name), "pid_%u", level + 1);
+ len = sizeof(struct pid) + level * sizeof(struct upid);
mutex_lock(&pid_caches_mutex);
- list_for_each_entry(pcache, &pid_caches_lh, list)
- if (pcache->nr_ids == nr_ids)
- goto out;
-
- pcache = kmalloc(sizeof(struct pid_cache), GFP_KERNEL);
- if (pcache == NULL)
- goto err_alloc;
-
- snprintf(pcache->name, sizeof(pcache->name), "pid_%d", nr_ids);
- cachep = kmem_cache_create(pcache->name,
- sizeof(struct pid) + (nr_ids - 1) * sizeof(struct upid),
- 0, SLAB_HWCACHE_ALIGN, NULL);
- if (cachep == NULL)
- goto err_cachep;
-
- pcache->nr_ids = nr_ids;
- pcache->cachep = cachep;
- list_add(&pcache->list, &pid_caches_lh);
-out:
+ /* Name collision forces to do allocation under mutex. */
+ if (!*pkc)
+ *pkc = kmem_cache_create(name, len, 0, SLAB_HWCACHE_ALIGN, 0);
mutex_unlock(&pid_caches_mutex);
- return pcache->cachep;
-
-err_cachep:
- kfree(pcache);
-err_alloc:
- mutex_unlock(&pid_caches_mutex);
- return NULL;
+ /* current can fail, but someone else can succeed. */
+ return READ_ONCE(*pkc);
}
static void proc_cleanup_work(struct work_struct *work)
@@ -80,9 +64,6 @@ static void proc_cleanup_work(struct work_struct *work)
pid_ns_release_proc(ns);
}
-/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
-#define MAX_PID_NS_LEVEL 32
-
static struct ucounts *inc_pid_namespaces(struct user_namespace *ns)
{
return inc_ucount(ns, current_euid(), UCOUNT_PID_NAMESPACES);
@@ -119,7 +100,7 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
idr_init(&ns->idr);
- ns->pid_cachep = create_pid_cachep(level + 1);
+ ns->pid_cachep = create_pid_cachep(level);
if (ns->pid_cachep == NULL)
goto out_free_idr;