linux-kernel - Re: [RFC PATCH 0/2] elevator: restore old io scheduler on failure in elevator

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Date:   Tue, 22 Nov 2022 13:24:46 +0100
From:   Christoph Hellwig <hch@....de>
To:     Jinlong Chen <nickyc975@....edu.cn>
Cc:     Christoph Hellwig <hch@....de>, axboe@...nel.dk,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] elevator: restore old io scheduler on failure
 in elevator_switch

On Tue, Nov 22, 2022 at 08:14:30PM +0800, Jinlong Chen wrote:
> Mostly failures specific to the intended io scheduler, like consuming more
> resources than the old one that the system can not afford. But sure it's
> rare, so do you think I should just correct the outdated document?

I'd be tempted to just documented the behavior, because I think the
chances are high that if switching to one schedule will fail that
switching back to the old one will fail as well.  I've done a quick
audit of all three schedulers, and unless I missed something there
are no other failure cases except for running out of memory.

Maybe a printk to document that switching the scheduler failed are
we aren't using any scheduler now might be useful, though.