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Message-ID: <b4ea5d02-40d9-9928-1094-9befed7ae4ff@linux.ibm.com>
Date:   Wed, 8 Jun 2022 13:54:38 +0530
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Subject: Re: [RFC PATCH v4 1/7] mm/demotion: Add support for explicit memory
 tiers
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To:     Ying Huang <ying.huang@intel.com>, linux-mm@kvack.org,
        akpm@linux-foundation.org
Cc:     Greg Thelen <gthelen@google.com>, Yang Shi <shy828301@gmail.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Tim C Chen <tim.c.chen@intel.com>,
        Brice Goglin <brice.goglin@gmail.com>,
        Michal Hocko <mhocko@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Hesham Almatary <hesham.almatary@huawei.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        Alistair Popple <apopple@nvidia.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Feng Tang <feng.tang@intel.com>,
        Jagdish Gediya <jvgediya@linux.ibm.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        David Rientjes <rientjes@google.com>
References: <CAAPL-u-dFp7PwPH6DfbYdnY8xaGsHz3tRQ0CPGVkiqURvdN8=A@mail.gmail.com>
 <20220527122528.129445-1-aneesh.kumar@linux.ibm.com>
 <20220527122528.129445-2-aneesh.kumar@linux.ibm.com>
 <604403db000ced33f997688ce82eaa43ed6c8bbe.camel@intel.com>
From:   Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>
In-Reply-To: <604403db000ced33f997688ce82eaa43ed6c8bbe.camel@intel.com>
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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 */
> 
>