linux-kernel - Re: [PATCH v2 3/5] x86: Kconfig: Remove CONFIG_NODES_SPAN_OTHER

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Message-ID: <910accd6-c491-acfd-237a-97edec7c0b42@os.amperecomputing.com>
Date:   Tue, 6 Aug 2019 16:47:12 +0000
From:   Hoan Tran OS <hoan@...amperecomputing.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Oscar Salvador <osalvador@...e.de>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        "David S . Miller" <davem@...emloft.net>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Open Source Submission <patches@...erecomputing.com>
Subject: Re: [PATCH v2 3/5] x86: Kconfig: Remove CONFIG_NODES_SPAN_OTHER_NODES

Hi Thomas,


On 7/15/19 11:43 AM, Thomas Gleixner wrote:
> On Thu, 11 Jul 2019, Hoan Tran OS wrote:
> 
>> Remove CONFIG_NODES_SPAN_OTHER_NODES as it's enabled
>> by default with NUMA.
> 
> As I told you before this does not mention that the option is now enabled
> even for x86(32bit) configurations which did not enable it before and does
> not longer depend on X86_64_ACPI_NUMA.

Agreed, let me add it into this patch description.

> 
> And there is still no rationale why this makes sense.
> 

As we know about the memmap_init_zone() function, it is used to 
initialize all pages. During initializing, early_pfn_in_nid() function 
makes sure the page is in the same node id. Otherwise, 
memmap_init_zone() only checks the page validity. It won't work with 
node memory spans across the others.

The option CONFIG_NODES_SPAN_OTHER_NODES is only used to enable 
early_pfn_in_nid() function.

It occurs during boot-time and won't affect the run-time performance.
And I saw the majority NUMA architectures enable this option by default 
with NUMA.

Thanks and Regards
Hoan


> Thanks,
> 
> 	tglx
>