blockgroup_lock.h: simplify definition of NR_BG_LOCKS

We can use ilog2() to more easily produce the desired NR_BG_LOCKS.  This
works because ilog2() is evaluated at compile-time when its argument is
a compile-time constant.

I did not change the chosen NR_BG_LOCKS values.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>

include/linux/blockgroup_lock.h

@@ -10,28 +10,10 @@
 #include <linux/cache.h>
 
 #ifdef CONFIG_SMP
-
-/*
- * We want a power-of-two.  Is there a better way than this?
- */
-
-#if NR_CPUS >= 32
-#define NR_BG_LOCKS	128
-#elif NR_CPUS >= 16
-#define NR_BG_LOCKS	64
-#elif NR_CPUS >= 8
-#define NR_BG_LOCKS	32
-#elif NR_CPUS >= 4
-#define NR_BG_LOCKS	16
-#elif NR_CPUS >= 2
-#define NR_BG_LOCKS	8
+#define NR_BG_LOCKS	(4 << ilog2(NR_CPUS < 32 ? NR_CPUS : 32))
 #else
-#define NR_BG_LOCKS	4
-#endif
-
-#else	/* CONFIG_SMP */
 #define NR_BG_LOCKS	1
-#endif	/* CONFIG_SMP */
+#endif
 
 struct bgl_lock {
 	spinlock_t lock;