Re: microblaze HAVE_MEMBLOCK_NODE_MAP dependency (was 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>,
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	<linux-arm-kernel@lists.infradead.org>,
	Oscar Salvador <osalvador@suse.de>,
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	Andrew Morton <akpm@linux-foundation.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"David S . Miller" <davem@davemloft.net>,
	"willy@infradead.org" <willy@infradead.org>
Subject: Re: microblaze HAVE_MEMBLOCK_NODE_MAP dependency (was Re: [PATCH v2 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA)
Date: Wed, 31 Jul 2019 17:21:29 +0300	[thread overview]
Message-ID: <20190731142129.GA24998@rapoport-lnx> (raw)
In-Reply-To: <20190731130037.GN9330@dhcp22.suse.cz>

On Wed, Jul 31, 2019 at 03:00:37PM +0200, Michal Hocko wrote:
> On Wed 31-07-19 15:26:32, Mike Rapoport wrote:
> > On Wed, Jul 31, 2019 at 01:40:16PM +0200, Michal Hocko wrote:
> > > On Wed 31-07-19 14:14:22, Mike Rapoport wrote:
> > > > 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.
> > > 
> > > I suppose you mean that microblaze is using
> > > sparse_memory_present_with_active_regions even without CONFIG_NUMA,
> > > right?
> > 
> > Yes.
> > 
> > > I have to confess I do not understand that code. What is the deal
> > > with setting node id there?
> > 
> > The sparse_memory_present_with_active_regions() iterates over
> > memblock.memory regions and uses the node id of each region as the
> > parameter to memory_present(). The assumption here is that sometime before
> > each region was assigned a proper non-negative node id. 
> > 
> > microblaze uses device tree for memory enumeration and the current FDT code
> > does memblock_add() that implicitly sets nid in memblock.memory regions to -1.
> > 
> > So in order to have proper node id passed to memory_present() microblaze
> > has to call memblock_set_node() before it can use
> > sparse_memory_present_with_active_regions().
> 
> I am sorry, but I still do not follow. Who is consuming that node id
> information when NUMA=n. In other words why cannot we simply do

We can, I think nobody cared to change it.

> diff --git a/arch/microblaze/mm/init.c b/arch/microblaze/mm/init.c
> index a015a951c8b7..3a47e8db8d1c 100644
> --- a/arch/microblaze/mm/init.c
> +++ b/arch/microblaze/mm/init.c
> @@ -175,14 +175,9 @@ void __init setup_memory(void)
>  
>  		start_pfn = memblock_region_memory_base_pfn(reg);
>  		end_pfn = memblock_region_memory_end_pfn(reg);
> -		memblock_set_node(start_pfn << PAGE_SHIFT,
> -				  (end_pfn - start_pfn) << PAGE_SHIFT,
> -				  &memblock.memory, 0);
> +		memory_present(0, start_pfn << PAGE_SHIFT, end_pfn << PAGE_SHIFT);

memory_present() expects pfns, the shift is not needed.

>  	}
>  
> -	/* XXX need to clip this if using highmem? */
> -	sparse_memory_present_with_active_regions(0);
> -
>  	paging_init();
>  }
>  
> -- 
> Michal Hocko
> SUSE Labs

-- 
Sincerely yours,
Mike.