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

From: Mel Gorman <mgorman@suse.de>
To: Waiman Long <waiman.long@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Linux-MM <linux-mm@kvack.org>, Nathan Zimmer <nzimmer@sgi.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Scott Norton <scott.norton@hp.com>,
	Daniel J Blueman <daniel@numascale.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 10/13] x86: mm: Enable deferred struct page initialisation on x86-64
Date: Sat, 25 Apr 2015 18:28:59 +0100	[thread overview]
Message-ID: <20150425172859.GE2449@suse.de> (raw)
In-Reply-To: <553A93BB.1010404@hp.com>

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?

-- 
Mel Gorman
SUSE Labs