scsi: sbitmap: Add sbitmap_calculate_shift() helper

Move code for calculating default shift into a public helper which can be
used by SCSI.

Link: https://lore.kernel.org/r/20210122023317.687987-7-ming.lei@redhat.com
Cc: Omar Sandoval <osandov@fb.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Cc: Ewan D. Milne <emilne@redhat.com>
Tested-by: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index c65ba88..3087e1f 100644 (file)
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -332,6 +332,24 @@ static inline int sbitmap_test_bit(struct sbitmap *sb, unsigned int bitnr)
        return test_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
 }
 
+static inline int sbitmap_calculate_shift(unsigned int depth)
+{
+       int     shift = ilog2(BITS_PER_LONG);
+
+       /*
+        * If the bitmap is small, shrink the number of bits per word so
+        * we spread over a few cachelines, at least. If less than 4
+        * bits, just forget about it, it's not going to work optimally
+        * anyway.
+        */
+       if (depth >= 4) {
+               while ((4U << shift) > depth)
+                       shift--;
+       }
+
+       return shift;
+}
+
 /**
  * sbitmap_show() - Dump &struct sbitmap information to a &struct seq_file.
  * @sb: Bitmap to show.

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 73da26a..47b3691 100644 (file)
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -87,19 +87,9 @@ int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
        unsigned int bits_per_word;
        unsigned int i;
 
-       if (shift < 0) {
-               shift = ilog2(BITS_PER_LONG);
-               /*
-                * If the bitmap is small, shrink the number of bits per word so
-                * we spread over a few cachelines, at least. If less than 4
-                * bits, just forget about it, it's not going to work optimally
-                * anyway.
-                */
-               if (depth >= 4) {
-                       while ((4U << shift) > depth)
-                               shift--;
-               }
-       }
+       if (shift < 0)
+               shift = sbitmap_calculate_shift(depth);
+
        bits_per_word = 1U << shift;
        if (bits_per_word > BITS_PER_LONG)
                return -EINVAL;