linux-kernel - Re: [PATCH 2/4] generic-smp: remove kmalloc usage

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Date:	Wed, 18 Feb 2009 17:05:35 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 2/4] generic-smp: remove kmalloc usage


* Rusty Russell <rusty@...tcorp.com.au> wrote:

> On Tuesday 17 February 2009 20:13:59 Ingo Molnar wrote:
> > We should not bend backwards trying to preserve that kmalloc() 
> > [and prove that it's safe and race-free] - i.e. the burden of 
> > proof is on the person insisting that it's needed, not on the 
> > person wanting to remove it.
> 
> Respectfully disagree.  The kmalloc has been there for a very long time,
> and doing fine AFAICT.

The kmalloc(GFP_ATOMIC) has been in kernel/smp.c for about half 
a year, since:

 |  commit 3d4422332711ef48ef0f132f1fcbfcbd56c7f3d1
 |  Author: Jens Axboe <jens.axboe@...cle.com>
 |  Date:   Thu Jun 26 11:21:34 2008 +0200
 |  Subject: [PATCH] Add generic helpers for arch IPI function calls

Which introduced kernel/smp.c to begin with. It got merged on 
July 15.

The precedecessor mechanism, smp_call_function*() on x86, used 
an on-kernel-stack buffer (and a half-wait mechanism), even in 
the async case, not a kmalloc().

I'm not sure where the "kmalloc has been there for a very long 
time" statement comes from. Are we talking about the same thing?

	Ingo
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