linux-kernel - Re: Memory allocator semantics

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Message-ID: <20140211120915.GP4250@linux.vnet.ibm.com>
Date:	Tue, 11 Feb 2014 04:09:16 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: Memory allocator semantics

On Tue, Feb 11, 2014 at 10:50:24AM +0200, Pekka Enberg wrote:
> Hi Paul,
> 
> On Sun, Feb 9, 2014 at 4:00 AM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > From what I can see, (A) works by accident, but is kind of useless because
> > you allocate and free the memory without touching it.  (B) and (C) are the
> > lightest touches I could imagine, and as you say, both are bad.  So I
> > believe that it is reasonable to prohibit (A).
> >
> > Or is there some use for (A) that I am missing?
> 
> So again, there's nothing in (A) that the memory allocator is
> concerned about.  kmalloc() makes no guarantees whatsoever about the
> visibility of "r1" across CPUs.  If you're saying that there's an
> implicit barrier between kmalloc() and kfree(), that's an unintended
> side-effect, not a design decision AFAICT.

Thank you.  That was what I suspected, and I believe that it is a
completely reasonable response to (A).

							Thanx, Paul

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