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Message-ID: <1332156655.18960.297.camel@twins>
Subject: Re: [RFC][PATCH 00/26] sched/numa
From: Peter Zijlstra <peterz@infradead.org>
To: Avi Kivity <avi@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
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        Suresh Siddha <suresh.b.siddha@intel.com>,
        Mike Galbraith <efault@gmx.de>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Lai Jiangshan <laijs@cn.fujitsu.com>, Dan Smith <danms@us.ibm.com>,
        Bharata B Rao <bharata.rao@gmail.com>,
        Lee Schermerhorn <Lee.Schermerhorn@hp.com>,
        Andrea Arcangeli <aarcange@redhat.com>, Rik van Riel <riel@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Date: Mon, 19 Mar 2012 12:30:55 +0100
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On Mon, 2012-03-19 at 12:12 +0100, Peter Zijlstra wrote:
> Also, if you go scan memory, you need some storage -- see how aa grows
> struct page, sure he wants to move that storage some place else, but the
> memory overhead is still there -- this means less memory to actually do
> useful stuff in (it also probably means more cache-misses since his
> proposed shadow array in pgdat is someplace else). 

Going by the sizes in aa's patch, that's 96M of my 16G box gone. That
puts HPC people in a rather awkward position of having to choose between
more memory and slightly smarter kernel. I'm thinking they're going to
opt for going the way they are now (hard affinity/userspace balancers)
and use the extra memory.

This even though typical MPI implementations use the multi-process
scheme, so the simple home-node approach I used works just fine for
them.