linux-kernel - Re: [PATCH 3/4] md: fix is_mddev

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Message-ID: <CALTww294r=ZFrmyK4=s8NMs4MZfdvZ-m6cLTQqXy+b+tW7gkBA@mail.gmail.com>
Date: Wed, 16 Apr 2025 17:44:42 +0800
From: Xiao Ni <xni@...hat.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: axboe@...nel.dk, song@...nel.org, linux-block@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org, yi.zhang@...wei.com, 
	yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH 3/4] md: fix is_mddev_idle()

On Wed, Apr 16, 2025 at 5:29 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> Hi,
>
> 在 2025/04/16 15:42, Yu Kuai 写道:
> > Hi,
> >
> > 在 2025/04/16 14:20, Xiao Ni 写道:
> >>> +static bool is_rdev_idle(struct md_rdev *rdev, bool init)
> >>> +{
> >>> +    unsigned long last_events = rdev->last_events;
> >>> +
> >>> +    if (!bdev_is_partition(rdev->bdev))
> >>> +        return true;
> >>
> >>
> >> For md array, I think is_rdev_idle is not useful. Because
> >> mddev->last_events must be increased while upper ios come in and idle
> >> will be set to false. For dm array, mddev->last_events can't work. So
> >> is_rdev_idle is for dm array. If member disk is one partition,
> >> is_rdev_idle alwasy returns true, and is_mddev_idle always return
> >> true. It's a bug here. Do we need to check bdev_is_partition here?
> >
> > is_rdev_idle() is not used for current array, for example:
> >
> > sda1 is used for array md0, and user doesn't issue IO to md0, while
> > user issues IO to sda2. In this case, is_mddev_idle() still fail for
> > array md0 because is_rdev_idle() fail.

Thanks very much for the explanation. It makes sense :)

>
> Perhaps the name is_rdev_holder_idle() is better.

Your suggestion is better. And it's better to add some comments before
this function.

But how about dm-raid? Can this patch work for dm-raid?

Regards
Xiao

>
> Thanks,
> Kuai
>
> >
> > This is just inherited from the old behaviour.
> >
> > Thanks,
> > Kuai
> >
> >>
> >> Best Regards
> >>
> >> Xiao
> >
> > .
> >
>