page-allocator: add inactive ratio calculation function of each zone

[sfrench/cifs-2.6.git] / lib / dec_and_lock.c

diff --git a/lib/dec_and_lock.c b/lib/dec_and_lock.c
index 2377af057d099ebd628bd9f7039cd4f54c9bf229..a65c314555416d9f1ea262455d1da313e1959902 100644 (file)
--- a/lib/dec_and_lock.c
+++ b/lib/dec_and_lock.c
@@ -3,10 +3,8 @@
 #include <asm/atomic.h>
 
 /*
- * This is an architecture-neutral, but slow,
- * implementation of the notion of "decrement
- * a reference count, and return locked if it
- * decremented to zero".
+ * This is an implementation of the notion of "decrement a
+ * reference count, and return locked if it decremented to zero".
  *
  * NOTE NOTE NOTE! This is _not_ equivalent to
  *
@@ -18,15 +16,15 @@
  *
  * because the spin-lock and the decrement must be
  * "atomic".
- *
- * This slow version gets the spinlock unconditionally,
- * and releases it if it isn't needed. Architectures
- * are encouraged to come up with better approaches,
- * this is trivially done efficiently using a load-locked
- * store-conditional approach, for example.
  */
 int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
 {
+#ifdef CONFIG_SMP
+       /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
+       if (atomic_add_unless(atomic, -1, 1))
+               return 0;
+#endif
+       /* Otherwise do it the slow way */
        spin_lock(lock);
        if (atomic_dec_and_test(atomic))
                return 1;