linux-kernel - Re: [PATCH -next v7 2/4] mm/zswap: skip invalid or unchanged parameter

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Message-ID: <20230326232508.GB19631@lst.de>
Date:   Mon, 27 Mar 2023 01:25:08 +0200
From:   Christoph Hellwig <hch@....de>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Liu Shixin <liushixin2@...wei.com>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH -next v7 2/4] mm/zswap: skip invalid or unchanged
 parameter

On Sun, Mar 26, 2023 at 01:53:27PM +0900, Sergey Senozhatsky wrote:
> > > +	if (kstrtobool(val, &res))
> > > +		return -EINVAL;
> > > +
> > > +	/* no change required */
> > > +	if (res == *(bool *)kp->arg)
> > > +		return 0;
> > 
> > Bool kernel param can be any of these letters 'YyTt1NnFf0'. Doing things
> > to kp->arg outside of kernel/params.c is not going to be easy, let's not
> > even try.
> 
> Please disregard my previous email. kp->arg is always true or false
> at this point. I'd still prefer to not do kp->arg in zswap.

The whole parameter handling in zswap is a mess and I don't really
have a good idea how to solve it all.

But for this "paramter not changed" case I think we can helper a lot
by adding a core moduleparam.h helper to encapsule it.  I.e.:

static inline bool param_bool_unchanged(bool val,
		const struct kernel_param *kp)

	return val == *(bool *)kp->arg);
}

and at least keep it out of zswap.