Re: [PATCH v2 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA

From: Mike Rapoport <rppt@linux.ibm.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Hoan Tran OS <hoan@os.amperecomputing.com>,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
	Paul Mackerras <paulus@samba.org>,
	"H . Peter Anvin" <hpa@zytor.com>,
	"sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>,
	"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	"x86@kernel.org" <x86@kernel.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Ingo Molnar <mingo@redhat.com>, Vlastimil Babka <vbabka@suse.cz>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Open Source Submission <patches@amperecomputing.com>,
	Pavel Tatashin <pavel.tatashin@microsoft.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Will Deacon <will.deacon@arm.com>, Borislav Petkov <bp@alien8.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	Oscar Salvador <osalvador@suse.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
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	"David S . Miller" <davem@davemloft.net>,
	"willy@infradead.org" <willy@infradead.org>
Subject: Re: [PATCH v2 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA
Date: Wed, 31 Jul 2019 14:14:22 +0300	[thread overview]
Message-ID: <20190731111422.GA14538@rapoport-lnx> (raw)
In-Reply-To: <20190731080309.GZ9330@dhcp22.suse.cz>

On Wed, Jul 31, 2019 at 10:03:09AM +0200, Michal Hocko wrote:
> On Wed 31-07-19 09:24:21, Mike Rapoport wrote:
> > [ sorry for a late reply too, somehow I missed this thread before ]
> > 
> > On Tue, Jul 30, 2019 at 10:14:15AM +0200, Michal Hocko wrote:
> > > [Sorry for a late reply]
> > > 
> > > On Mon 15-07-19 17:55:07, Hoan Tran OS wrote:
> > > > Hi,
> > > > 
> > > > On 7/12/19 10:00 PM, Michal Hocko wrote:
> > > [...]
> > > > > Hmm, I thought this was selectable. But I am obviously wrong here.
> > > > > Looking more closely, it seems that this is indeed only about
> > > > > __early_pfn_to_nid and as such not something that should add a config
> > > > > symbol. This should have been called out in the changelog though.
> > > > 
> > > > Yes, do you have any other comments about my patch?
> > > 
> > > Not really. Just make sure to explicitly state that
> > > CONFIG_NODES_SPAN_OTHER_NODES is only about __early_pfn_to_nid and that
> > > doesn't really deserve it's own config and can be pulled under NUMA.
> > > 
> > > > > Also while at it, does HAVE_MEMBLOCK_NODE_MAP fall into a similar
> > > > > bucket? Do we have any NUMA architecture that doesn't enable it?
> > > > > 
> > 
> > HAVE_MEMBLOCK_NODE_MAP makes huge difference in node/zone initialization
> > sequence so it's not only about a singe function.
> 
> The question is whether we want to have this a config option or enable
> it unconditionally for each NUMA system.

We can make it 'default NUMA', but we can't drop it completely because
microblaze uses sparse_memory_present_with_active_regions() which is
unavailable when HAVE_MEMBLOCK_NODE_MAP=n.

> > > > As I checked with arch Kconfig files, there are 2 architectures, riscv 
> > > > and microblaze, do not support NUMA but enable this config.
> > 
> > My take would be that riscv will support NUMA some day.
> >  
> > > > And 1 architecture, alpha, supports NUMA but does not enable this config.
> > 
> > alpha's NUMA support is BROKEN for more than a decade now, I doubt it'll
> > ever get fixed.
> 
> I can see Al has marked it BROKEN in 2005. Maybe time to rip it out?
> Although it doesn't seem to be a lot of code in arch/alpha at first
> glance so maybe not worth an effort.
> -- 
> Michal Hocko
> SUSE Labs
> 

-- 
Sincerely yours,
Mike.