Trim another pointer from struct lock_object (and thus from struct mtx and

struct sx).  Instead of storing a direct pointer to a our lock_class
struct in lock_object, reserve 4 bits in the lo_flags field to serve as an
index into a global lock_classes array that contains pointers to the lock
classes.  Only debugging code such as WITNESS or INVARIANTS checks and KTR
logging need to access the lock_class member, so this shouldn't add any
overhead to production kernels.  It might add some slight overhead to
kernels using those debug options however.

As with the previous set of changes to lock_object, this is going to
completely obliterate the kernel ABI, so be sure to recompile all your
modules.

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/kern/kern_sx.c b/sys/kern/kern_sx.c
index 7a14de0..d24e4de 100644
--- a/sys/kern/kern_sx.c
+++ b/sys/kern/kern_sx.c
@@ -83,9 +83,9 @@ sx_init(struct sx *sx, const char *description)
 	KASSERT((lock->lo_flags & LO_INITIALIZED) == 0,
 	    ("sx lock %s %p already initialized", description, sx));
 	bzero(sx, sizeof(*sx));
-	lock->lo_class = &lock_class_sx;
+	lock->lo_flags = LOCK_CLASS_SX << LO_CLASSSHIFT;
 	lock->lo_type = lock->lo_name = description;
-	lock->lo_flags = LO_WITNESS | LO_RECURSABLE | LO_SLEEPABLE |
+	lock->lo_flags |= LO_WITNESS | LO_RECURSABLE | LO_SLEEPABLE |
 	    LO_UPGRADABLE;
 	sx->sx_lock = mtx_pool_find(mtxpool_lockbuilder, sx);
 	sx->sx_cnt = 0;