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

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Message-ID: <553E970E.2040406@hp.com>
Date:	Mon, 27 Apr 2015 16:07:42 -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 04/25/2015 01:28 PM, Mel Gorman wrote:
> On Fri, Apr 24, 2015 at 03:04:27PM -0400, Waiman Long wrote:
>>>> Within a NUMA node, however, we can split the
>>>> memory initialization to 2 or more local CPUs if the memory size is
>>>> big enough.
>>>>
>>> I considered it but discarded the idea. It'd be more complex to setup and
>>> the two CPUs could simply end up contending on the same memory bus as
>>> well as contending on zone->lock.
>>>
>> I don't think we need that now. However, we may have to consider
>> this when one day even a single node can have TBs of memory unless
>> we move to a page size larger than 4k.
>>
> We'll cross that bridge when we come to it. I suspect there is more room
> for improvement in the initialisation that would be worth trying before
> resorting to more threads. With more threads there is a risk that we hit
> memory bus contention and a high risk that it actually is worse due to
> contending on zone->lock when freeing the pages.
>
> In the meantime, do you mind updating the before/after figures for your
> test machine with this series please?
>

I will test the latest patch once I got my hand on a 12TB machine.

Cheers,
Longman
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