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

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Message-Id: <200902191501.47564.rusty@rustcorp.com.au>
Date:	Thu, 19 Feb 2009 15:01:46 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
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

On Thursday 19 February 2009 02:35:35 Ingo Molnar wrote:
> 
> * 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

Oops, yes.

So if we care about the kmalloc, why didn't we see benchmarks when we
switched from the x86 smp_call_function_mask to the generic one?  Or did
I just miss them (there's nothing in the git commit).

Now, I think the current patch is quite neat and may not been benchmarks to
justify it, but it'd still be nice if it were faster, but noone seems to know.

Rusty.
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