Use kernel provided mutex owner

To reduce mutex footprint, we detect the existence of owner in kernel mutex,
and rely on it if it exists.

Note that before Linux 3.0, mutex owner is of type thread_info. Also note
that, in Linux 3.18, the condition for owner is changed from
CONFIG_DEBUG_MUTEXES || CONFIG_SMP to
CONFIG_DEBUG_MUTEXES || CONFIG_MUTEX_SPIN_ON_OWNER

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #540

diff --git a/config/spl-build.m4 b/config/spl-build.m4
index b9c04a95e01d60aa6d92d81e49836d200085f542..55453c822e7d5d6d680c87c3029839a8e1682fd0 100644 (file)
--- a/config/spl-build.m4
+++ b/config/spl-build.m4
@@ -44,6 +44,7 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
        SPL_AC_USLEEP_RANGE
        SPL_AC_KMEM_CACHE_ALLOCFLAGS
        SPL_AC_WAIT_ON_BIT
+       SPL_AC_MUTEX_OWNER
 ])
 
 AC_DEFUN([SPL_AC_MODULE_SYMVERS], [
@@ -1447,3 +1448,31 @@ AC_DEFUN([SPL_AC_WAIT_ON_BIT], [
                AC_MSG_RESULT(no)
        ])
 ])
+
+dnl #
+dnl # Check whether mutex has owner with task_struct type.
+dnl #
+dnl # Note that before Linux 3.0, mutex owner is of type thread_info.
+dnl #
+dnl # Note that in Linux 3.18, the condition for owner is changed from
+dnl # defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP) to
+dnl # defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_MUTEX_SPIN_ON_OWNER)
+dnl #
+AC_DEFUN([SPL_AC_MUTEX_OWNER], [
+       AC_MSG_CHECKING([whether mutex has owner])
+       tmp_flags="$EXTRA_KCFLAGS"
+       EXTRA_KCFLAGS="-Werror"
+       SPL_LINUX_TRY_COMPILE([
+               #include <linux/mutex.h>
+       ],[
+               DEFINE_MUTEX(m);
+               struct task_struct *t __attribute__ ((unused));
+               t = m.owner;
+       ],[
+               AC_MSG_RESULT(yes)
+               AC_DEFINE(HAVE_MUTEX_OWNER, 1, [yes])
+       ],[
+               AC_MSG_RESULT(no)
+       ])
+       EXTRA_KCFLAGS="$tmp_flags"
+])

diff --git a/include/sys/mutex.h b/include/sys/mutex.h
index fba35f3f9813b0bcb695d48b2c1a86bf1e4f0f68..31923522308e8391ad2e2ba6dec94345f9eb7a98 100644 (file)
--- a/include/sys/mutex.h
+++ b/include/sys/mutex.h
@@ -40,7 +40,10 @@ typedef enum {
 typedef struct {
        struct mutex            m_mutex;
        spinlock_t              m_lock; /* used for serializing mutex_exit */
+#ifndef HAVE_MUTEX_OWNER
+       /* only when kernel doesn't have owner */
        kthread_t               *m_owner;
+#endif
 #ifdef CONFIG_LOCKDEP
        kmutex_type_t           m_type;
 #endif /* CONFIG_LOCKDEP */
@@ -51,16 +54,28 @@ typedef struct {
 static inline void
 spl_mutex_set_owner(kmutex_t *mp)
 {
+       /*
+        * kernel will handle its owner, so we don't need to do anything if it
+        * is defined.
+        */
+#ifndef HAVE_MUTEX_OWNER
        mp->m_owner = current;
+#endif
 }
 
 static inline void
 spl_mutex_clear_owner(kmutex_t *mp)
 {
+#ifndef HAVE_MUTEX_OWNER
        mp->m_owner = NULL;
+#endif
 }
 
+#ifdef HAVE_MUTEX_OWNER
+#define        mutex_owner(mp)         (ACCESS_ONCE(MUTEX(mp)->owner))
+#else
 #define        mutex_owner(mp)         (ACCESS_ONCE((mp)->m_owner))
+#endif
 #define        mutex_owned(mp)         (mutex_owner(mp) == current)
 #define        MUTEX_HELD(mp)          mutex_owned(mp)
 #define        MUTEX_NOT_HELD(mp)      (!MUTEX_HELD(mp))