btrfs: reduce chunk_map lookups in btrfs_map_block()

Currently we're calling btrfs_num_copies() before btrfs_get_chunk_map() in
btrfs_map_block(). But btrfs_num_copies() itself does a chunk map lookup
to be able to calculate the number of copies.

So split out the code getting the number of copies from btrfs_num_copies()
into a helper called btrfs_chunk_map_num_copies() and directly call it
from btrfs_map_block() and btrfs_num_copies().

This saves us one rbtree lookup per btrfs_map_block() invocation.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index e07452207426aac9c628330de375abde220feb5d..8f340ad1d938456df052c377b18f0dcbb85dbc49 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5781,11 +5781,31 @@ void btrfs_mapping_tree_free(struct btrfs_fs_info *fs_info)
        write_unlock(&fs_info->mapping_tree_lock);
 }
 
+static int btrfs_chunk_map_num_copies(const struct btrfs_chunk_map *map)
+{
+       enum btrfs_raid_types index = btrfs_bg_flags_to_raid_index(map->type);
+
+       if (map->type & BTRFS_BLOCK_GROUP_RAID5)
+               return 2;
+
+       /*
+        * There could be two corrupted data stripes, we need to loop retry in
+        * order to rebuild the correct data.
+        *
+        * Fail a stripe at a time on every retry except the stripe under
+        * reconstruction.
+        */
+       if (map->type & BTRFS_BLOCK_GROUP_RAID6)
+               return map->num_stripes;
+
+       /* Non-RAID56, use their ncopies from btrfs_raid_array. */
+       return btrfs_raid_array[index].ncopies;
+}
+
 int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
 {
        struct btrfs_chunk_map *map;
-       enum btrfs_raid_types index;
-       int ret = 1;
+       int ret;
 
        map = btrfs_get_chunk_map(fs_info, logical, len);
        if (IS_ERR(map))
@@ -5797,22 +5817,7 @@ int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
                 */
                return 1;
 
-       index = btrfs_bg_flags_to_raid_index(map->type);
-
-       /* Non-RAID56, use their ncopies from btrfs_raid_array. */
-       if (!(map->type & BTRFS_BLOCK_GROUP_RAID56_MASK))
-               ret = btrfs_raid_array[index].ncopies;
-       else if (map->type & BTRFS_BLOCK_GROUP_RAID5)
-               ret = 2;
-       else if (map->type & BTRFS_BLOCK_GROUP_RAID6)
-               /*
-                * There could be two corrupted data stripes, we need
-                * to loop retry in order to rebuild the correct data.
-                *
-                * Fail a stripe at a time on every retry except the
-                * stripe under reconstruction.
-                */
-               ret = map->num_stripes;
+       ret = btrfs_chunk_map_num_copies(map);
        btrfs_free_chunk_map(map);
        return ret;
 }
@@ -6462,14 +6467,14 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
        io_geom.stripe_index = 0;
        io_geom.op = op;
 
-       num_copies = btrfs_num_copies(fs_info, logical, fs_info->sectorsize);
-       if (io_geom.mirror_num > num_copies)
-               return -EINVAL;
-
        map = btrfs_get_chunk_map(fs_info, logical, *length);
        if (IS_ERR(map))
                return PTR_ERR(map);
 
+       num_copies = btrfs_chunk_map_num_copies(map);
+       if (io_geom.mirror_num > num_copies)
+               return -EINVAL;
+
        map_offset = logical - map->start;
        io_geom.raid56_full_stripe_start = (u64)-1;
        max_len = btrfs_max_io_len(map, map_offset, &io_geom);