Re: [PATCH V3] Btrfs: enchanse raid1/10 balance heuristic

[Dmitrii Tcvetkov <demfloro@demfloro.ru>]

On Sat, 30 Dec 2017 23:32:04 +0300
Timofey Titovets <nefelim4ag@gmail.com> wrote:

> Currently btrfs raid1/10 balancer balance requests to mirrors,
> based on pid % num of mirrors.
> 
> Make logic understood:
>  - if one of underline devices are non rotational
>  - Queue leght to underline devices
> 
> By default try use pid % num_mirrors guessing, but:
>  - If one of mirrors are non rotational, repick optimal to it
>  - If underline mirror have less queue leght then optimal,
>    repick to that mirror
> 
> For avoid round-robin request balancing,
> lets round down queue leght:
>  - By 8 for rotational devs
>  - By 2 for all non rotational devs
> 
> Changes:
>   v1 -> v2:
>     - Use helper part_in_flight() from genhd.c
>       to get queue lenght
>     - Move guess code to guess_optimal()
>     - Change balancer logic, try use pid % mirror by default
>       Make balancing on spinning rust if one of underline devices
>       are overloaded
>   v2 -> v3:
>     - Fix arg for RAID10 - use sub_stripes, instead of num_stripes
> 
> Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>

Reviewed-by: Dmitrii Tcvetkov <demfloro@demfloro.ru>