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Subject: Re: [RFC][PATCH 00/26] sched/numa
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Mon, 19 Mar 2012 20:13:16 +0100
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To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Avi Kivity <avi@redhat.com>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>, Paul Turner <pjt@google.com>, 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>, Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>, linux-kernel@vger.kernel.org, linux-mm@kvack.org

On Mon, 2012-03-19 at 14:57 +0100, Andrea Arcangeli wrote:
> With your code they will get -ENOMEM from split_vma and a slowdown in
> all regular page faults and vma mangling operations, before they run
> out of memory...=20

But why would you want to create that many vmas? If you're going to call
sys_numa_mbind() at object level you're doing it wrong.=20

Typical usage would be to call it on the chunks your allocator asks from
the system. Depending on how your application decomposes this is per
thread or per thread-pool.

But again, who is writing such large threaded apps. The shared address
space thing is cute, but the shared address space thing is also the
bottleneck. Sharing mmap_sem et al across the entire machine has been
enough reason not to use threads for plenty people.


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