Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Subject: Re: [PATCH -next v7 2/4] mm/zswap: skip invalid or unchanged
 parameter
To:     Christoph Hellwig <hch@lst.de>,
        Sergey Senozhatsky <senozhatsky@chromium.org>
References: <20230325071420.2246461-1-liushixin2@huawei.com>
 <20230325071420.2246461-3-liushixin2@huawei.com>
 <20230326031723.GD3269998@google.com> <20230326045327.GE3269998@google.com>
 <20230326232508.GB19631@lst.de>
CC:     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>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
From:   Liu Shixin <liushixin2@huawei.com>
Message-ID: <c5dc155f-a53f-dd8c-86a2-c59e0839314b@huawei.com>
Date:   Mon, 27 Mar 2023 09:22:36 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101
 Thunderbird/45.7.1
MIME-Version: 1.0
In-Reply-To: <20230326232508.GB19631@lst.de>
Content-Type: text/plain; charset="windows-1252"
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 2023/3/27 7:25, Christoph Hellwig wrote:
> 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.
Thanks for your advice. I will try this way.
>
> .
>