linux-kernel - Re: [RFC PATCH 1/2] workqueue: Introduce PF_WQ_RESCUE

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Date:   Tue,  1 Aug 2023 11:04:20 +0100
From:   Aaron Tomlin <atomlin@...mlin.com>
To:     peterz@...radead.org, tj@...nel.org
Cc:     atomlin@...mlin.com, jiangshanlai@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] workqueue: Introduce PF_WQ_RESCUE_WORKER

> Is the implication that PF_flags are considered ABI? We've been changing
> them quite a bit over the years.

Hi Peter, Tejun,

I never assumed they were.

In this context, one should always check the Linux kernel source code first
i.e. do not assume what is exported via /proc/[PID]/stat will be stable/or
consistent between releases.

> Also, while we have a few spare bits atm, we used to be nearly out for a
> while, and I just don't think this is sane usage of them. We don't use PF
> flags just for userspace.

Fair statement.

Albeit, I suspect it would still be useful for user-mode to easily
differentiate between a kworker and a rescuer kworker. According to
create_worker(), we do make it clear the difference between a CPU-specific
and unbound kworker by way of the task's name. Looking at init_rescuer() a
rescuer kworker is simply given the name of its workqueue. Would you
consider modifying the rescuer's task's name so it is prefixed with
"kworker/r-%s" and then include the workqueue's name e.g.
"kworker/r-ext4-rsv-conver" acceptable?

Kind regards,
-- 
Aaron Tomlin