[PATCH 07/12] bitmap: add small_const_nbits() optimization for bitmap_bitremap()

[Yury Norov <yury.norov@gmail.com>]

When 'bits' is less than BITS_PER_LONG, we can remap a bit inline.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
 include/linux/bitmap.h | 36 ++++++++++++++++++++++++++++++++++--
 lib/bitmap.c           | 15 ++-------------
 2 files changed, 36 insertions(+), 15 deletions(-)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 486451b80339..da5030a99af5 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -163,6 +163,8 @@ void __bitmap_replace(unsigned long *dst,
 		      const unsigned long *mask, unsigned int nbits);
 void __bitmap_remap(unsigned long *dst, const unsigned long *src,
 		const unsigned long *old, const unsigned long *new, unsigned int nbits);
+int __bitmap_bitremap(int oldbit,
+		const unsigned long *old, const unsigned long *new, int nbits);
 bool __bitmap_intersects(const unsigned long *bitmap1,
 			 const unsigned long *bitmap2, unsigned int nbits);
 bool __bitmap_subset(const unsigned long *bitmap1,
@@ -214,8 +216,6 @@ int bitmap_parselist(const char *buf, unsigned long *maskp,
 int bitmap_parselist_user(const char __user *ubuf, unsigned int ulen,
 			unsigned long *dst, int nbits);
 
-int bitmap_bitremap(int oldbit,
-		const unsigned long *old, const unsigned long *new, int bits);
 void bitmap_onto(unsigned long *dst, const unsigned long *orig,
 		const unsigned long *relmap, unsigned int bits);
 void bitmap_fold(unsigned long *dst, const unsigned long *orig,
@@ -733,6 +733,38 @@ static inline void bitmap_remap(unsigned long *dst, const unsigned long *src,
 	__bitmap_remap(dst, src, old, new, nbits);
 }
 
+/**
+ * bitmap_bitremap - Apply map defined by a pair of bitmaps to a single bit
+ *	@oldbit: bit position to be mapped
+ *	@old: defines domain of map
+ *	@new: defines range of map
+ *	@nbits: number of bits in each of these bitmaps
+ *
+ * A special case of bitmap_remap(), when a single bit remapping is needed.
+ *
+ * Returns: position of remapped bit
+ */
+static inline int bitmap_bitremap(int oldbit,
+		const unsigned long *old, const unsigned long *new, int nbits)
+{
+	if (small_const_nbits(nbits)) {
+		unsigned int w, n;
+
+		if ((*old & BIT(oldbit)) == 0 ||
+		    (*old & BITMAP_LAST_WORD_MASK(nbits)) == 0 ||
+		    (*new & BITMAP_LAST_WORD_MASK(nbits)) == 0 ||
+		    ((*new ^ *old) & BITMAP_LAST_WORD_MASK(nbits)) == 0) {
+			return oldbit;
+		}
+
+		w = bitmap_weight(new, nbits);
+		n = bitmap_weight(old, oldbit);
+		return find_nth_bit(new, nbits, n % w);
+	}
+
+	return __bitmap_bitremap(oldbit, old, new, nbits);
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __LINUX_BITMAP_H */
diff --git a/lib/bitmap.c b/lib/bitmap.c
index 2ac48d9bcbc0..9ecdc74cb6b4 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -1014,18 +1014,7 @@ void __bitmap_remap(unsigned long *dst, const unsigned long *src,
 }
 EXPORT_SYMBOL(__bitmap_remap);
 
-/**
- * bitmap_bitremap - Apply map defined by a pair of bitmaps to a single bit
- *	@oldbit: bit position to be mapped
- *	@old: defines domain of map
- *	@new: defines range of map
- *	@bits: number of bits in each of these bitmaps
- *
- * A special case of bitmap_remap(), when a single bit remapping is needed.
- *
- * Returns: position of remapped bit
- */
-int bitmap_bitremap(int oldbit, const unsigned long *old,
+int __bitmap_bitremap(int oldbit, const unsigned long *old,
 				const unsigned long *new, int bits)
 {
 	int w = bitmap_weight(new, bits);
@@ -1035,7 +1024,7 @@ int bitmap_bitremap(int oldbit, const unsigned long *old,
 	else
 		return find_nth_bit(new, bits, n % w);
 }
-EXPORT_SYMBOL(bitmap_bitremap);
+EXPORT_SYMBOL(__bitmap_bitremap);
 
 #ifdef CONFIG_NUMA
 /**
-- 
2.39.2