percpu-refcount: one bit is enough for REF_STATUS

percpu-refcount currently reserves two lowest bits of its percpu
pointer to indicate its state; however, only one bit is used for
PCPU_REF_DEAD.

Simplify it by removing PCPU_STATUS_BITS/MASK and testing
PCPU_REF_DEAD directly.  This also allows the compiler to choose a
more efficient instruction depending on the architecture.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Christoph Lameter <cl@linux-foundation.org>

2 files changed, 2 insertions, 4 deletions

diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 5d8920e23073..bfdeb0d48e21 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -88,12 +88,10 @@ static inline void percpu_ref_kill(struct percpu_ref *ref)
         return percpu_ref_kill_and_confirm(ref, NULL);
 }
 
-#define PCPU_STATUS_BITS        2
-#define PCPU_STATUS_MASK        ((1 << PCPU_STATUS_BITS) - 1)
 #define PCPU_REF_PTR            0
 #define PCPU_REF_DEAD           1
 
-#define REF_STATUS(count)       (((unsigned long) count) & PCPU_STATUS_MASK)
+#define REF_STATUS(count)       (((unsigned long) count) & PCPU_REF_DEAD)
 
 /**
  * percpu_ref_get - increment a percpu refcount
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 963b7034a51b..17bce2bccc14 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -96,7 +96,7 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
 
         /* Mask out PCPU_REF_DEAD */
         pcpu_count = (unsigned __percpu *)
-                (((unsigned long) pcpu_count) & ~PCPU_STATUS_MASK);
+                (((unsigned long) pcpu_count) & ~PCPU_REF_DEAD);
 
         for_each_possible_cpu(cpu)
                 count += *per_cpu_ptr(pcpu_count, cpu);