linux-kernel - Re: [PATCH] pblk: fix max

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Date:   Thu, 7 Mar 2019 16:57:50 +0100
From:   Matias Bjørling <mb@...htnvm.io>
To:     Javier González <javier@...igon.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] pblk: fix max_io calculation

On 3/7/19 1:18 PM, Javier González wrote:
> When calculating the maximun I/O size allowed into the buffer, consider
> the write size (ws_opt) used by the write thread in order to cover the
> case in which, due to flushes, the mem and subm pointers are disaligned
> by (ws_opt - 1). This case currently translates into a stall when
> an I/O of the largest possible size is submitted.
> 
> Fixes: f9f9d1ae2c66 ("lightnvm: pblk: prevent stall due to wb threshold")
> 
> Signed-off-by: Javier González <javier@...igon.com>
> ---
> 
> Matias: Can you apply this as a fix to 5.1. This is a case I missed when fixing
> the wb threshold, which is also scheduled for 5.1
> 
> Thanks,
> Javier
> 
>   drivers/lightnvm/pblk-rl.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/lightnvm/pblk-rl.c b/drivers/lightnvm/pblk-rl.c
> index b014957dde0b..a5f8bc2defbc 100644
> --- a/drivers/lightnvm/pblk-rl.c
> +++ b/drivers/lightnvm/pblk-rl.c
> @@ -233,10 +233,15 @@ void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold)
>   	/* To start with, all buffer is available to user I/O writers */
>   	rl->rb_budget = budget;
>   	rl->rb_user_max = budget;
> -	rl->rb_max_io = threshold ? (budget - threshold) : (budget - 1);
>   	rl->rb_gc_max = 0;
>   	rl->rb_state = PBLK_RL_HIGH;
>   
> +	/* Maximize I/O size and ansure that back threshold is respected */
> +	if (threshold)
> +		rl->rb_max_io = budget - pblk->min_write_pgs_data - threshold;
> +	else
> +		rl->rb_max_io = budget - pblk->min_write_pgs_data - 1;
> +
>   	atomic_set(&rl->rb_user_cnt, 0);
>   	atomic_set(&rl->rb_gc_cnt, 0);
>   	atomic_set(&rl->rb_space, -1);
> 

Hi Jens,

If possible, could you please pick this one up for 5.1? It fixes a 
previous patch that was introduced in 5.1 that should fix a stall, but 
didn't quite catch it.

Thank you,
-Matias