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

From: Waiman Long
Date: Mon Apr 27 2015 - 16:07:52 EST

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.

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