Btrfs: don't do extra bitmap search in one bit case

When we make ctl->unit allocations from a bitmap there is no point in searching
for the next 0 in the bitmap.  If we've found a bit we're done and can just exit
the loop.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 15 insertions, 13 deletions

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index e10c9668e4fd..0948d34cb84a 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -1730,7 +1730,7 @@ static void bitmap_set_bits(struct btrfs_free_space_ctl *ctl,
  */
 static int search_bitmap(struct btrfs_free_space_ctl *ctl,
                          struct btrfs_free_space *bitmap_info, u64 *offset,
-                         u64 *bytes)
+                         u64 *bytes, bool for_alloc)
 {
         unsigned long found_bits = 0;
         unsigned long max_bits = 0;
@@ -1742,7 +1742,8 @@ static int search_bitmap(struct btrfs_free_space_ctl *ctl,
          * Skip searching the bitmap if we don't have a contiguous section that
          * is large enough for this allocation.
          */
-        if (bitmap_info->max_extent_size &&
+        if (for_alloc &&
+            bitmap_info->max_extent_size &&
             bitmap_info->max_extent_size < *bytes) {
                 *bytes = bitmap_info->max_extent_size;
                 return -1;
@@ -1753,6 +1754,10 @@ static int search_bitmap(struct btrfs_free_space_ctl *ctl,
         bits = bytes_to_bits(*bytes, ctl->unit);
 
         for_each_set_bit_from(i, bitmap_info->bitmap, BITS_PER_BITMAP) {
+                if (for_alloc && bits == 1) {
+                        found_bits = 1;
+                        break;
+                }
                 next_zero = find_next_zero_bit(bitmap_info->bitmap,
                                                BITS_PER_BITMAP, i);
                 extent_bits = next_zero - i;
@@ -1824,7 +1829,7 @@ find_free_space(struct btrfs_free_space_ctl *ctl, u64 *offset, u64 *bytes,
                 if (entry->bitmap) {
                         u64 size = *bytes;
 
-                        ret = search_bitmap(ctl, entry, &tmp, &size);
+                        ret = search_bitmap(ctl, entry, &tmp, &size, true);
                         if (!ret) {
                                 *offset = tmp;
                                 *bytes = size;
@@ -1885,7 +1890,8 @@ again:
         search_start = *offset;
         search_bytes = ctl->unit;
         search_bytes = min(search_bytes, end - search_start + 1);
-        ret = search_bitmap(ctl, bitmap_info, &search_start, &search_bytes);
+        ret = search_bitmap(ctl, bitmap_info, &search_start, &search_bytes,
+                            false);
         if (ret < 0 || search_start != *offset)
                 return -EINVAL;
 
@@ -1930,7 +1936,7 @@ again:
                 search_start = *offset;
                 search_bytes = ctl->unit;
                 ret = search_bitmap(ctl, bitmap_info, &search_start,
-                                    &search_bytes);
+                                    &search_bytes, false);
                 if (ret < 0 || search_start != *offset)
                         return -EAGAIN;
 
@@ -2685,7 +2691,7 @@ static u64 btrfs_alloc_from_bitmap(struct btrfs_block_group_cache *block_group,
         search_start = min_start;
         search_bytes = bytes;
 
-        err = search_bitmap(ctl, entry, &search_start, &search_bytes);
+        err = search_bitmap(ctl, entry, &search_start, &search_bytes, true);
         if (err) {
                 if (search_bytes > *max_extent_size)
                         *max_extent_size = search_bytes;
@@ -3262,7 +3268,7 @@ static int trim_bitmaps(struct btrfs_block_group_cache *block_group,
                 }
 
                 bytes = minlen;
-                ret2 = search_bitmap(ctl, entry, &start, &bytes);
+                ret2 = search_bitmap(ctl, entry, &start, &bytes, false);
                 if (ret2 || start >= end) {
                         spin_unlock(&ctl->tree_lock);
                         mutex_unlock(&ctl->cache_writeout_mutex);
@@ -3415,7 +3421,7 @@ u64 btrfs_find_ino_for_alloc(struct btrfs_root *fs_root)
                 u64 count = 1;
                 int ret;
 
-                ret = search_bitmap(ctl, entry, &offset, &count);
+                ret = search_bitmap(ctl, entry, &offset, &count, true);
                 /* Logic error; Should be empty if it can't find anything */
                 ASSERT(!ret);
 
@@ -3600,10 +3606,6 @@ again:
 
         bytes_added = add_bytes_to_bitmap(ctl, bitmap_info, offset, bytes);
 
-        /* We used the newly allocated info, set the max_extent_size to bytes */
-        if (!info)
-                bitmap_info->max_extent_size = bytes_added;
-
         bytes -= bytes_added;
         offset += bytes_added;
         spin_unlock(&ctl->tree_lock);
@@ -3647,7 +3649,7 @@ have_info:
 
                 bit_off = offset;
                 bit_bytes = ctl->unit;
-                ret = search_bitmap(ctl, info, &bit_off, &bit_bytes);
+                ret = search_bitmap(ctl, info, &bit_off, &bit_bytes, false);
                 if (!ret) {
                         if (bit_off == offset) {
                                 ret = 1;