On Wed, Jun 07, 2017 at 06:09:33PM +0000, Sargun Dhillon wrote:
> This patch is a small performance optimization to get rid of a spin
> lock, where instead an atomic64_t can be used.
>
> Signed-off-by: Sargun Dhillon <sargun@xxxxxxxxx>
[snip]
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 017b67d..0123974 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -2417,9 +2417,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
> fs_info->fs_devices->total_devices++;
> fs_info->fs_devices->total_rw_bytes += device->total_bytes;
>
> - spin_lock(&fs_info->free_chunk_lock);
> - fs_info->free_chunk_space += device->total_bytes;
> - spin_unlock(&fs_info->free_chunk_lock);
> + atomic64_add(device->total_bytes, &fs_info->free_chunk_space);
>
> if (!blk_queue_nonrot(q))
> fs_info->fs_devices->rotating = 1;
> @@ -2874,9 +2872,7 @@ int btrfs_remove_chunk(struct btrfs_trans_handle *trans,
> mutex_lock(&fs_info->chunk_mutex);
> btrfs_device_set_bytes_used(device,
> device->bytes_used - dev_extent_len);
> - spin_lock(&fs_info->free_chunk_lock);
> - fs_info->free_chunk_space += dev_extent_len;
> - spin_unlock(&fs_info->free_chunk_lock);
> + atomic64_add(dev_extent_len, &fs_info->free_chunk_space);
> btrfs_clear_space_info_full(fs_info);
> mutex_unlock(&fs_info->chunk_mutex);
> }
> @@ -4409,9 +4405,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
> btrfs_device_set_total_bytes(device, new_size);
> if (device->writeable) {
> device->fs_devices->total_rw_bytes -= diff;
> - spin_lock(&fs_info->free_chunk_lock);
> - fs_info->free_chunk_space -= diff;
> - spin_unlock(&fs_info->free_chunk_lock);
> + atomic64_sub(diff, &fs_info->free_chunk_space);
> }
> mutex_unlock(&fs_info->chunk_mutex);
>
> @@ -4535,9 +4529,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
> btrfs_device_set_total_bytes(device, old_size);
> if (device->writeable)
> device->fs_devices->total_rw_bytes += diff;
> - spin_lock(&fs_info->free_chunk_lock);
> - fs_info->free_chunk_space += diff;
> - spin_unlock(&fs_info->free_chunk_lock);
> + atomic64_add(diff, &fs_info->free_chunk_space);
> mutex_unlock(&fs_info->chunk_mutex);
> }
> return ret;
> @@ -4882,9 +4874,7 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
> btrfs_device_set_bytes_used(map->stripes[i].dev, num_bytes);
> }
>
> - spin_lock(&info->free_chunk_lock);
> - info->free_chunk_space -= (stripe_size * map->num_stripes);
> - spin_unlock(&info->free_chunk_lock);
> + atomic64_sub((stripe_size * map->num_stripes), &info->free_chunk_space);
Can you please get rid of the extra parentheses around the
multiplication here? Also curious if you were able to measure any sort
of performance difference. Besides that,
Reviewed-by: Omar Sandoval <osandov@xxxxxx>
>
> free_extent_map(em);
> check_raid56_incompat_flag(info, type);
> @@ -6684,10 +6674,8 @@ static int read_one_dev(struct btrfs_fs_info *fs_info,
> device->in_fs_metadata = 1;
> if (device->writeable && !device->is_tgtdev_for_dev_replace) {
> device->fs_devices->total_rw_bytes += device->total_bytes;
> - spin_lock(&fs_info->free_chunk_lock);
> - fs_info->free_chunk_space += device->total_bytes -
> - device->bytes_used;
> - spin_unlock(&fs_info->free_chunk_lock);
> + atomic64_add(device->total_bytes - device->bytes_used,
> + &fs_info->free_chunk_space);
> }
> ret = 0;
> return ret;
> --
> 2.9.3
>
> --
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