linux-kernel - Re: [RFC v1 2/2] mm: SLUB Freelist randomization

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Message-ID: <alpine.DEB.2.20.1605181323260.14349@east.gentwo.org>
Date:	Wed, 18 May 2016 13:24:57 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Thomas Garnier <thgarnie@...gle.com>
cc:	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Pranith Kumar <bobby.prani@...il.com>,
	David Howells <dhowells@...hat.com>, Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	David Woodhouse <David.Woodhouse@...el.com>,
	Petr Mladek <pmladek@...e.com>,
	Kees Cook <keescook@...omium.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, gthelen@...gle.com,
	kernel-hardening@...ts.openwall.com
Subject: Re: [RFC v1 2/2] mm: SLUB Freelist randomization

0.On Wed, 18 May 2016, Thomas Garnier wrote:

> slab_test, before:
> 10000 times kmalloc(8) -> 67 cycles kfree -> 101 cycles
> 10000 times kmalloc(16) -> 68 cycles kfree -> 109 cycles
> 10000 times kmalloc(32) -> 76 cycles kfree -> 119 cycles
> 10000 times kmalloc(64) -> 88 cycles kfree -> 114 cycles

> After:
> 10000 times kmalloc(8) -> 60 cycles kfree -> 74 cycles
> 10000 times kmalloc(16) -> 63 cycles kfree -> 78 cycles
> 10000 times kmalloc(32) -> 72 cycles kfree -> 85 cycles
> 10000 times kmalloc(64) -> 91 cycles kfree -> 99 cycles

Erm... The fastpath was not touched and the tests primarily exercise the
fastpath. This is likely some artifact of code placement by the compiler?