From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f50.google.com (mail-pb0-f50.google.com [209.85.160.50]) by kanga.kvack.org (Postfix) with ESMTP id BC1D86B0031 for ; Sun, 5 Jan 2014 23:32:31 -0500 (EST) Received: by mail-pb0-f50.google.com with SMTP id rr13so17950647pbb.23 for ; Sun, 05 Jan 2014 20:32:31 -0800 (PST) Received: from LGEMRELSE1Q.lge.com (LGEMRELSE1Q.lge.com. [156.147.1.111]) by mx.google.com with ESMTP id gx4si53506422pbc.21.2014.01.05.20.32.28 for ; Sun, 05 Jan 2014 20:32:30 -0800 (PST) Date: Mon, 6 Jan 2014 13:32:37 +0900 From: Joonsoo Kim Subject: Re: [PATCH 0/9] re-shrink 'struct page' when SLUB is on. Message-ID: <20140106043237.GE696@lge.com> References: <20140103180147.6566F7C1@viggo.jf.intel.com> <20140103141816.20ef2a24c8adffae040e53dc@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140103141816.20ef2a24c8adffae040e53dc@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Dave Hansen , linux-mm@kvack.org, linux-kernel@vger.kernel.org, penberg@kernel.org, cl@linux-foundation.org On Fri, Jan 03, 2014 at 02:18:16PM -0800, Andrew Morton wrote: > On Fri, 03 Jan 2014 10:01:47 -0800 Dave Hansen wrote: > > > This is a minor update from the last version. The most notable > > thing is that I was able to demonstrate that maintaining the > > cmpxchg16 optimization has _some_ value. > > > > Otherwise, the code changes are just a few minor cleanups. > > > > --- > > > > SLUB depends on a 16-byte cmpxchg for an optimization which > > allows it to not disable interrupts in its fast path. This > > optimization has some small but measurable benefits: > > > > http://lkml.kernel.org/r/52B345A3.6090700@sr71.net > > So really the only significant benefit from the cmpxchg16 is with > cache-cold eight-byte kmalloc/kfree? 8% faster in this case? But with > cache-hot kmalloc/kfree the benefit of cmpxchg16 is precisely zero. Hello, I guess that cmpxchg16 is not used in this cache-hot kmalloc/kfree test, because kfree would be done in free fast-path. In this case, this_cpu_cmpxchg_double() would be called, so you cannot find any effect of cmpxchg16. Thanks. > > This is really weird and makes me suspect a measurement glitch. > > Even if this 8% is real, it's unclear that it's worth all the > complexity the cmpxchg16 adds. > > It would be really useful (hint :)) if we were to know exactly where > that 8% is coming from - perhaps it's something which is not directly > related to the cmpxchg16, and we can fix it separately. > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org