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Date:   Mon, 27 Mar 2023 01:25:08 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Sergey Senozhatsky <senozhatsky@chromium.org>
Cc:     Liu Shixin <liushixin2@huawei.com>,
        Seth Jennings <sjenning@redhat.com>,
        Dan Streetman <ddstreet@ieee.org>,
        Vitaly Wool <vitaly.wool@konsulko.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Christoph Hellwig <hch@lst.de>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH -next v7 2/4] mm/zswap: skip invalid or unchanged
 parameter
Message-ID: <20230326232508.GB19631@lst.de>
References: <20230325071420.2246461-1-liushixin2@huawei.com> <20230325071420.2246461-3-liushixin2@huawei.com> <20230326031723.GD3269998@google.com> <20230326045327.GE3269998@google.com>
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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.