linux-kernel - Re: [PATCH stable] block/mq-deadline: fix different priority request on the same zone

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Date: Thu, 16 May 2024 07:45:21 -0600
From: Bart Van Assche <bvanassche@....org>
To: Wu Bo <bo.wu@...o.com>, linux-kernel@...r.kernel.org
Cc: Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
 Wu Bo <wubo.oduw@...il.com>, stable@...r.kernel.org,
 Damien Le Moal <dlemoal@...nel.org>
Subject: Re: [PATCH stable] block/mq-deadline: fix different priority request
 on the same zone

On 5/16/24 03:28, Wu Bo wrote:
> Zoned devices request sequential writing on the same zone. That means
> if 2 requests on the saem zone, the lower pos request need to dispatch
> to device first.
> While different priority has it's own tree & list, request with high
> priority will be disptch first.
> So if requestA & requestB are on the same zone. RequestA is BE and pos
> is X+0. ReqeustB is RT and pos is X+1. RequestB will be disptched before
> requestA, which got an ERROR from zoned device.
> 
> This is found in a practice scenario when using F2FS on zoned device.
> And it is very easy to reproduce:
> 1. Use fsstress to run 8 test processes
> 2. Use ionice to change 4/8 processes to RT priority

Hi Wu,

I agree that there is a problem related to the interaction of I/O
priority and zoned storage. A solution with a lower runtime overhead
is available here:
https://lore.kernel.org/linux-block/20231218211342.2179689-1-bvanassche@acm.org/T/#me97b088c535278fe3d1dc5846b388ed58aa53f46

Are you OK with that alternative solution?

Thanks,

Bart.