Re: [PATCH 4/9] btrfs: check reclaim_size in need_preemptive_reclaim

[Nikolay Borisov <nborisov@suse.com>]

On 30.09.20 г. 23:01 ч., Josef Bacik wrote:
> If we're flushing space for tickets then we have
> space_info->reclaim_size set and we do not need to do background
> reclaim.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

I'm fine with this but check my remak below.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  fs/btrfs/space-info.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
> index 98207ea57a3d..518749093bc5 100644
> --- a/fs/btrfs/space-info.c
> +++ b/fs/btrfs/space-info.c
> @@ -805,6 +805,13 @@ static inline int need_preemptive_reclaim(struct btrfs_fs_info *fs_info,
>  	if ((space_info->bytes_used + space_info->bytes_reserved) >= thresh)
>  		return 0;
>  
> +	/*
> +	 * We have tickets queued, bail so we don't compete with the async
> +	 * flushers.
> +	 */
> +	if (space_info->reclaim_size)
> +		return 0;
> +

nit: So where do we draw the line if this check should be in this
function or in __reserve_bytes so that we eliminate the case where a
preemptive reclaim is scheduled only to return instantly because of
tickets. Though the 'if' in __reserve_bytes is getting slitghly out of
hand :)

>  	if (!btrfs_calc_reclaim_metadata_size(fs_info, space_info))
>  		return 0;
>  
>