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

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Date:   Wed, 08 Jun 2022 16:27:59 +0800
From:   Ying Huang <ying.huang@...el.com>
To:     Aneesh Kumar K V <aneesh.kumar@...ux.ibm.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 Wed, 2022-06-08 at 13:54 +0530, Aneesh Kumar K V wrote:
> 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?

Yes.  We don't need to panic system for this.

Best Regards,
Huang, Ying

> > > +
> > > +	/*
> > > +	 * 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 */
> > 
> > 
>