btrfs: reduce block group critical section in btrfs_add_reserved_bytes()

We are doing some things inside the block group's critical section that
are relevant only to the space_info: updating the space_info counters
bytes_reserved and bytes_may_use as well as trying to grant tickets
(calling btrfs_try_granting_tickets()), and this later can take some
time. So move all those updates to outside the block group's critical
section and still inside the space_info's critical section. Like this
we keep the block group's critical section only for block group updates
and can help reduce contention on a block group's lock.

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

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 856bda9c99d95ce4ca6f410cd07d3b5478c2ffce..b964eacc1610247647cd1a91c8807405608ea5d0 100644 (file)
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -3813,22 +3813,26 @@ int btrfs_add_reserved_bytes(struct btrfs_block_group *cache,
        spin_lock(&cache->lock);
        if (cache->ro) {
                ret = -EAGAIN;
-               goto out;
+               goto out_error;
        }
 
        if (btrfs_block_group_should_use_size_class(cache)) {
                size_class = btrfs_calc_block_group_size_class(num_bytes);
                ret = btrfs_use_block_group_size_class(cache, size_class, force_wrong_size_class);
                if (ret)
-                       goto out;
+                       goto out_error;
        }
+
        cache->reserved += num_bytes;
-       space_info->bytes_reserved += num_bytes;
+       if (delalloc)
+               cache->delalloc_bytes += num_bytes;
+
        trace_btrfs_space_reservation(cache->fs_info, "space_info",
                                      space_info->flags, num_bytes, 1);
+       spin_unlock(&cache->lock);
+
+       space_info->bytes_reserved += num_bytes;
        btrfs_space_info_update_bytes_may_use(space_info, -ram_bytes);
-       if (delalloc)
-               cache->delalloc_bytes += num_bytes;
 
        /*
         * Compression can use less space than we reserved, so wake tickets if
@@ -3836,7 +3840,11 @@ int btrfs_add_reserved_bytes(struct btrfs_block_group *cache,
         */
        if (num_bytes < ram_bytes)
                btrfs_try_granting_tickets(space_info);
-out:
+       spin_unlock(&space_info->lock);
+
+       return 0;
+
+out_error:
        spin_unlock(&cache->lock);
        spin_unlock(&space_info->lock);
        return ret;