linux-kernel - Re: [RFC PATCH v4 1/7] mm/demotion: Add support for explicit memory tiers

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Message-ID: <b4ea5d02-40d9-9928-1094-9befed7ae4ff@linux.ibm.com>
Date:   Wed, 8 Jun 2022 13:54:38 +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:     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: [RFC PATCH v4 1/7] mm/demotion: Add support for explicit memory
 tiers

On 6/8/22 12:46 PM, Ying Huang wrote:
> On Fri, 2022-05-27 at 17:55 +0530, Aneesh Kumar K.V wrote:
> 
> [snip]
> 
>>
>> +static int __init memory_tier_init(void)
>> +{
>> +	int ret;
>> +
>> +	ret = subsys_system_register(&memory_tier_subsys, memory_tier_attr_groups);
>> +	if (ret)
>> +		panic("%s() failed to register subsystem: %d\n", __func__, ret);
> 
> I don't think we should go panic for failing to register subsys and
> device for memory tiers.  Just pr_err() should be enough.
> 

So you are suggesting we continue to work with memory tiers with no 
userspace interface?

>> +
>> +	/*
>> +	 * Register only default memory tier to hide all empty
>> +	 * memory tier from sysfs.
>> +	 */
>> +	ret = register_memory_tier(DEFAULT_MEMORY_TIER);
>> +	if (ret)
>> +		panic("%s() failed to register memory tier: %d\n", __func__, ret);
>> +
>> +	/*
>> +	 * CPU only nodes are not part of memoty tiers.
>> +	 */
>> +	memory_tiers[DEFAULT_MEMORY_TIER]->nodelist = node_states[N_MEMORY];
>> +
>> +	return 0;
>> +}
>> +subsys_initcall(memory_tier_init);
>> +
>> +#endif	/* CONFIG_TIERED_MEMORY */
> 
>