linux-kernel - Re: [PATCH 19/40] autonuma: alloc/free/init sched

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Message-ID: <20120630051000.GF3975@localhost.localdomain>
Date:	Sat, 30 Jun 2012 01:10:01 -0400
From:	Konrad Rzeszutek Wilk <konrad@...nok.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Alex Shi <alex.shi@...el.com>,
	Mauricio Faria de Oliveira <mauricfo@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Don Morris <don.morris@...com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 19/40] autonuma: alloc/free/init sched_autonuma

On Thu, Jun 28, 2012 at 02:55:59PM +0200, Andrea Arcangeli wrote:
> This is where the dynamically allocated sched_autonuma structure is
> being handled.
> 
> The reason for keeping this outside of the task_struct besides not
> using too much kernel stack, is to only allocate it on NUMA
> hardware. So the not NUMA hardware only pays the memory of a pointer
> in the kernel stack (which remains NULL at all times in that case). 

.. snip..
> +	if (unlikely(alloc_task_autonuma(tsk, orig, node)))
> +		/* free_thread_info() undoes arch_dup_task_struct() too */
> +		goto out_thread_info;
>  

That looks (without seeing the implementation) and from reading the git
commit, like that on non-NUMA machines it would fail - and end up
stop the creation of a task.

Perhaps a better name for the function: alloc_always_task_autonuma
since the function (at least from the description of this patch) will
always succeed. Perhaps even remove the:
"if unlikely(..)" bit?

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