libext2fs: optimize rb_get_bmap_range() for mostly allocated bmaps

This optimizies the CPU utilization of the rb_get_bmap_range()
function when most of the bitmap is allocated.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>

diff --git a/lib/ext2fs/blkmap64_rb.c b/lib/ext2fs/blkmap64_rb.c
index eb56c85..7196e90 100644 (file)
--- a/lib/ext2fs/blkmap64_rb.c
+++ b/lib/ext2fs/blkmap64_rb.c
@@ -721,6 +721,7 @@ static errcode_t rb_get_bmap_range(ext2fs_generic_bitmap bitmap,
        struct rb_node *parent = NULL, *next, **n;
        struct ext2fs_rb_private *bp;
        struct bmap_rb_extent *ext;
+       int count;
        __u64 pos;
 
        bp = (struct ext2fs_rb_private *) bitmap->private;
@@ -748,14 +749,32 @@ static errcode_t rb_get_bmap_range(ext2fs_generic_bitmap bitmap,
                ext = ext2fs_rb_entry(parent, struct bmap_rb_extent, node);
 
                pos = ext->start;
-               if (pos < start)
+               count = ext->count;
+               if (pos >= start + num)
+                       break;
+               if (pos < start) {
+                       count -= start - pos;
+                       if (count < 0)
+                               continue;
                        pos = start;
-
-               while (pos < (ext->start + ext->count)) {
-                       if ((pos - start) >= num)
-                               return 0;
+               }
+               if (pos + count > start + num)
+                       count = start + num - pos;
+
+               while (count > 0) {
+                       if ((count >= 8) &&
+                           ((pos - start) % 8) == 0) {
+                               int nbytes = count >> 3;
+                               int offset = (pos - start) >> 3;
+
+                               memset(out + offset, 0xFF, nbytes);
+                               pos += nbytes << 3;
+                               count -= nbytes << 3;
+                               continue;
+                       }
                        ext2fs_fast_set_bit64((pos - start), out);
                        pos++;
+                       count--;
                }
        }
        return 0;