Re: [PATCH 3/3] blk-wbt: throttle discards like background writes

[Christoph Hellwig]

> -static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb, bool is_kswapd)
> +static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb, bool is_trim,
> +                                       bool is_kswapd)
>  {
> -     return &rwb->rq_wait[is_kswapd];
> +     if (is_trim)
> +             return &rwb->rq_wait[WBT_REQ_DISCARD];
> +     else if (is_kswapd)
> +             return &rwb->rq_wait[WBT_REQ_KSWAPD];
> +     else
> +             return &rwb->rq_wait[WBT_REQ_BG];
>  }

Wouldn't it be more useful to pass a enum wbt_flag here?

Or just have a wbt_flag_to_wait_idx helper and do the array indexing
in the callers?

>  {
>       const int op = bio_op(bio);
>  
> -     /*
> -      * If not a WRITE, do nothing
> -      */
> -     if (op != REQ_OP_WRITE)
> -             return false;
> +     if (op == REQ_OP_WRITE) {
> +             /*
> +              * Don't throttle WRITE_ODIRECT
> +              */
> +             if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) ==
> +                 (REQ_SYNC | REQ_IDLE))
> +                     return false;
>  
> -     /*
> -      * Don't throttle WRITE_ODIRECT
> -      */
> -     if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) == (REQ_SYNC | REQ_IDLE))
> -             return false;
> +             return true;
> +     } else if (op == REQ_OP_DISCARD)
> +             return true;

what about:

        switch (bio_op(bio)) {
        case REQ_OP_WRITE:
                /*
                 * Don't throttle WRITE_ODIRECT
                 */
                if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) ==
                    (REQ_SYNC | REQ_IDLE))
                        return false;
                /*FALLTHROUGH*/
        case REQ_OP_DISCARD:
                return true;
        default:
                return false;