linux-kernel - Re: [RFC PATCH] mdadm: Add parameter for bitmap chunk threshold

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Message-ID: <20221012091700.0000695b@linux.intel.com>
Date:   Wed, 12 Oct 2022 09:17:00 +0200
From:   Mariusz Tkaczyk <mariusz.tkaczyk@...ux.intel.com>
To:     Jonathan Derrick <jonathan.derrick@...ux.dev>
Cc:     Song Liu <song@...nel.org>, <linux-raid@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, jonathan.derrick@...idigm.com,
        jonathanx.sk.derrick@...el.com
Subject: Re: [RFC PATCH] mdadm: Add parameter for bitmap chunk threshold

On Thu,  6 Oct 2022 16:08:38 -0600
Jonathan Derrick <jonathan.derrick@...ux.dev> wrote:

> Adds parameter to mdadm create, grow, and build similar to the delay
> parameter, that specifies a chunk threshold. This value will instruct
> the kernel, in-tandem with the delay timer, to flush the bitmap after
> every N chunks have been dirtied. This can be used in-addition to the
> delay parameter and complements it.
> 
> This requires an addition to the bitmap superblock and version increment.

Hello Jonathan,
To provide that to parameter to bitmap we are updating bitmap superblock, right?
Why we need to define it in config then? I someone wants to change that
should use --grow. Am I correct?

The "threshold" is not a context property, it should be added to struct shape.
Ideally, we can extract bitmap properties to separate struct and pass it around.

And I would like to have IMSM support if that is possible.

Thanks,
Mariusz