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

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Message-ID: <6d74b4a9.5489.1849f42de2d.Coremail.nickyc975@zju.edu.cn>
Date:   Tue, 22 Nov 2022 20:14:30 +0800 (GMT+08:00)
From:   "Jinlong Chen" <nickyc975@....edu.cn>
To:     "Christoph Hellwig" <hch@....de>
Cc:     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 Fri, Nov 18, 2022 at 08:09:52PM +0800, Jinlong Chen wrote:
> > elevator_switch contains the fallback logic in sq era, but it was removed
> > when moving to mq (commit: a1ce35fa49852db60fc6e268038530be533c5b15),
> > leaving the document mismatched with the behavior. As far as I can see,
> > restoring the old io scheduler is more reasonable than just leaving the
> > scheduler none, hence there is the series.
> 
> What failure scenariou can you think off where switching to the intended
> schedule fails, but switching back to the previous one will succeed?

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rare, so do you think I should just correct the outdated document?

Thanks!
Jinlong Chen