linux-kernel - Re: [PATCH 10/13] x86: mm: Enable deferred struct page initialisation on x86-64

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Date:	Fri, 24 Apr 2015 10:35:49 -0400
From:	Waiman Long <waiman.long@...com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>, Nathan Zimmer <nzimmer@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Scott Norton <scott.norton@...com>,
	Daniel J Blueman <daniel@...ascale.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/13] x86: mm: Enable deferred struct page initialisation
 on x86-64

On 04/23/2015 05:23 AM, Mel Gorman wrote:
> On Wed, Apr 22, 2015 at 04:45:00PM -0700, Andrew Morton wrote:
>> On Wed, 22 Apr 2015 18:07:50 +0100 Mel Gorman<mgorman@...e.de>  wrote:
>>
>>> --- a/arch/x86/Kconfig
>>> +++ b/arch/x86/Kconfig
>>> @@ -32,6 +32,7 @@ config X86
>>>   	select HAVE_UNSTABLE_SCHED_CLOCK
>>>   	select ARCH_SUPPORTS_NUMA_BALANCING if X86_64
>>>   	select ARCH_SUPPORTS_INT128 if X86_64
>>> +	select ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT if X86_64&&  NUMA
>> Put this in the "config X86_64" section and skip the "X86_64&&"?
>>
> Done.
>
>> Can we omit the whole defer_meminit= thing and permanently enable the
>> feature?  That's simpler, provides better test coverage and is, we
>> hope, faster.
>>
> Yes. The intent was to have a workaround if there were any failures like
> Waiman's vmalloc failures in an earlier version but they are bugs that
> should be fixed.
>
>> And can this be used on non-NUMA?  Presumably that won't speed things
>> up any if we're bandwidth limited but again it's simpler and provides
>> better coverage.
> Nothing prevents it. There is less opportunity for parallelism but
> improving coverage is desirable.
>

Memory access latency can be more than double for local vs. remote node 
memory. Bandwidth can also be much lower depending on what kind of 
interconnect is between the 2 nodes. So it is better to do it in a 
NUMA-aware way. Within a NUMA node, however, we can split the memory 
initialization to 2 or more local CPUs if the memory size is big enough.

Cheers,
Longman
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