linux-kernel - Re: [PATCH v6 03/13] mm/demotion: Return error on write to numa

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Date:   Mon, 13 Jun 2022 09:05:59 +0530
From:   Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
To:     Ying Huang <ying.huang@...el.com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org
Cc:     Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>,
        Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim C Chen <tim.c.chen@...el.com>,
        Brice Goglin <brice.goglin@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hesham Almatary <hesham.almatary@...wei.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Feng Tang <feng.tang@...el.com>,
        Jagdish Gediya <jvgediya@...ux.ibm.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v6 03/13] mm/demotion: Return error on write to
 numa_demotion sysfs

On 6/13/22 8:56 AM, Ying Huang wrote:
> On Fri, 2022-06-10 at 19:22 +0530, Aneesh Kumar K.V wrote:
>> With CONFIG_MIGRATION disabled return EINVAL on write.
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
>> ---
>>   mm/memory-tiers.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
>> index 9c6b40d7e0bf..c3123a457d90 100644
>> --- a/mm/memory-tiers.c
>> +++ b/mm/memory-tiers.c
>> @@ -105,6 +105,9 @@ static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
>>   {
>>   	ssize_t ret;
>>   
>>
>> +	if (!IS_ENABLED(CONFIG_MIGRATION))
>> +		return -EINVAL;
>> +
> 
> How about enclose numa_demotion_enabled_xxx related code with CONFIG_MIGRATION?
> 

IIUC there is a desire to use IS_ENABLED() in the kernel instead of 
#ifdef since that helps in more compile time checks. Because there are 
no dead codes during compile now with IS_ENABLED().

W.r.t leaving the sysfs file visible even when CONFIG_MIGRATION is 
disabled, I was thinking it gives better visibility into numa_demotion 
status. I could switch to hide numa_demotion file if that is desirable.

>>   	ret = kstrtobool(buf, &numa_demotion_enabled);
>>   	if (ret)
>>   		return ret;
> 

-aneesh