[PATCH 1/1] mlock: split the shmlock_user_lock spinlock into per user_struct spinlock

rajman mekaco
2012-05-03T17:35:25Z

The user_shm_lock and user_shm_unlock functions use a single global
spinlock for protecting the user->locked_shm.

This is an overhead for multiple CPUs calling this code even if they
are having different user_struct.

Remove the global shmlock_user_lock and introduce and use a new
spinlock inside of the user_struct structure.

Signed-off-by: rajman mekaco <rajman.mekaco@gmail.com>
---
include/linux/sched.h | 1 +
kernel/user.c | 1 +
mm/mlock.c | 10 ++++------
3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 81a173c..c661cfd 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -720,6 +720,7 @@ struct user_struct {
unsigned long mq_bytes; /* How many bytes can be allocated to mqueue? */
#endif
unsigned long locked_shm; /* How many pages of mlocked shm ? */
+ spinlock_t shmlock_user_lock; /* Protects locked_shm */

#ifdef CONFIG_KEYS
struct key *uid_keyring; /* UID specific keyring */
diff --git a/kernel/user.c b/kernel/user.c
index 71dd236..ca7f423 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -169,6 +169,7 @@ struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
} else {
uid_hash_insert(new, hashent);
up = new;
+ spin_lock_init(&new->shmlock_user_lock);
}
spin_unlock_irq(&uidhash_lock);
}
diff --git a/mm/mlock.c b/mm/mlock.c
index ef726e8..11a78a6 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -593,8 +593,6 @@ SYSCALL_DEFINE0(munlockall)
* Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
* shm segments) get accounted against the user_struct instead.
*/
-static DEFINE_SPINLOCK(shmlock_user_lock);
-
int user_shm_lock(size_t size, struct user_struct *user)
{
unsigned long lock_limit, locked;
@@ -605,7 +603,7 @@ int user_shm_lock(size_t size, struct user_struct *user)
if (lock_limit == RLIM_INFINITY)
allowed = 1;
lock_limit >>= PAGE_SHIFT;
- spin_lock(&shmlock_user_lock);
+ spin_lock(&user->shmlock_user_lock);
if (!allowed &&
locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
goto out;
@@ -613,14 +611,14 @@ int user_shm_lock(size_t size, struct user_struct *user)
user->locked_shm += locked;
allowed = 1;
out:
- spin_unlock(&shmlock_user_lock);
+ spin_unlock(&user->shmlock_user_lock);
return allowed;
}

void user_shm_unlock(size_t size, struct user_struct *user)
{
- spin_lock(&shmlock_user_lock);
+ spin_lock(&user->shmlock_user_lock);
user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
- spin_unlock(&shmlock_user_lock);
+ spin_unlock(&user->shmlock_user_lock);
free_uid(user);
}
--
1.7.5.4