linux-kernel - Re: [RFC][PATCH 00/26] sched/numa

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Date:	Mon, 19 Mar 2012 20:13:16 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Dan Smith <danms@...ibm.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][PATCH 00/26] sched/numa

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... 

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. 

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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