From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f46.google.com (mail-pa0-f46.google.com [209.85.220.46]) by kanga.kvack.org (Postfix) with ESMTP id CB0D66B0036 for ; Fri, 3 Jan 2014 17:18:19 -0500 (EST) Received: by mail-pa0-f46.google.com with SMTP id kp14so14506909pab.33 for ; Fri, 03 Jan 2014 14:18:19 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTP id dv5si47012667pbb.73.2014.01.03.14.18.18 for ; Fri, 03 Jan 2014 14:18:18 -0800 (PST) Date: Fri, 3 Jan 2014 14:18:16 -0800 From: Andrew Morton Subject: Re: [PATCH 0/9] re-shrink 'struct page' when SLUB is on. Message-Id: <20140103141816.20ef2a24c8adffae040e53dc@linux-foundation.org> In-Reply-To: <20140103180147.6566F7C1@viggo.jf.intel.com> References: <20140103180147.6566F7C1@viggo.jf.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, penberg@kernel.org, cl@linux-foundation.org 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. 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