Re: [PATCH v2 02/11] btrfs: track ordered bytes instead of just dio ordered bytes

[Nikolay Borisov <nborisov@suse.com>]

On 8.10.20 г. 23:48 ч., Josef Bacik wrote:
> We track dio_bytes because the shrink delalloc code needs to know if we
> have more DIO in flight than we have normal buffered IO.  The reason for
> this is because we can't "flush" DIO, we have to just wait on the
> ordered extents to finish.
> 
> However this is true of all ordered extents.  If we have more ordered
> space outstanding than dirty pages we should be waiting on ordered
> extents.  We already are ok on this front technically, because we always
> do a FLUSH_DELALLOC_WAIT loop, but I want to use the ordered counter in
> the preemptive flushing code as well, so change this to count all
> ordered bytes instead of just DIO ordered bytes.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

<snip>

> --- a/fs/btrfs/space-info.c
> +++ b/fs/btrfs/space-info.c
> @@ -489,7 +489,7 @@ static void shrink_delalloc(struct btrfs_fs_info *fs_info,
>  {
>  	struct btrfs_trans_handle *trans;
>  	u64 delalloc_bytes;
> -	u64 dio_bytes;
> +	u64 ordered_bytes;
>  	u64 items;
>  	long time_left;
>  	int loops;
> @@ -513,8 +513,8 @@ static void shrink_delalloc(struct btrfs_fs_info *fs_info,
>  
>  	delalloc_bytes = percpu_counter_sum_positive(
>  						&fs_info->delalloc_bytes);
> -	dio_bytes = percpu_counter_sum_positive(&fs_info->dio_bytes);
> -	if (delalloc_bytes == 0 && dio_bytes == 0) {
> +	ordered_bytes = percpu_counter_sum_positive(&fs_info->ordered_bytes);
> +	if (delalloc_bytes == 0 && ordered_bytes == 0) {
>  		if (trans)
>  			return;
>  		if (wait_ordered)
Does it make sense to wait for ordered even if wait_ordered is true and
ordered_bytes is 0 ? Perhaps this condition can be simplified to just :

if (delalloc_bytes == 0 && ordered_bytes == 0) return;

<snip>