From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964958AbWD0LlL (ORCPT ); Thu, 27 Apr 2006 07:41:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964960AbWD0LlK (ORCPT ); Thu, 27 Apr 2006 07:41:10 -0400 Received: from mailhost.tue.nl ([131.155.2.19]:35837 "EHLO mailhost.tue.nl") by vger.kernel.org with ESMTP id S964958AbWD0LlI (ORCPT ); Thu, 27 Apr 2006 07:41:08 -0400 Message-ID: <4450ADCF.8040005@etpmod.phys.tue.nl> Date: Thu, 27 Apr 2006 13:41:03 +0200 From: Bart Hartgers User-Agent: Thunderbird 1.5 (X11/20060111) MIME-Version: 1.0 To: Arjan van de Ven Cc: Adrian Bunk , Pekka J Enberg , Nick Piggin , =?ISO-8859-1?Q?J=F6rn_Engel?= , Hua Zhong , linux-kernel@vger.kernel.org, akpm@osdl.org Subject: Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL) References: <1146046118.7016.5.camel@laptopd505.fenrus.org> <1146049414.7016.9.camel@laptopd505.fenrus.org> <20060426110656.GD29108@wohnheim.fh-wedel.de> <445061DC.5030008@yahoo.com.au> <1146120640.2894.1.camel@laptopd505.fenrus.org> <20060427083157.GD3570@stusta.de> <1146127273.2894.21.camel@laptopd505.fenrus.org> <20060427085614.GE3570@stusta.de> <1146128885.2894.27.camel@laptopd505.fenrus.org> In-Reply-To: <1146128885.2894.27.camel@laptopd505.fenrus.org> Content-Type: multipart/mixed; boundary="------------050403060107080906010809" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------050403060107080906010809 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Arjan van de Ven wrote: > On Thu, 2006-04-27 at 10:56 +0200, Adrian Bunk wrote: >> On Thu, Apr 27, 2006 at 10:41:12AM +0200, Arjan van de Ven wrote: >>> On Thu, 2006-04-27 at 10:31 +0200, Adrian Bunk wrote: >>>> On Thu, Apr 27, 2006 at 08:50:40AM +0200, Arjan van de Ven wrote: >>>>> On Thu, 2006-04-27 at 09:28 +0300, Pekka J Enberg wrote: >>>>>> On Thu, 27 Apr 2006, Nick Piggin wrote: >>>>>>> Not to dispute your conclusions or method, but I think doing a >>>>>>> defconfig or your personal config might be more representative >>>>>>> of % size increase of text that will actually be executed. And >>>>>>> that is the expensive type of text. >>>>>> True but I was under the impression that Arjan thought we'd get text >>>>>> savings with GCC 4.1 by making kfree() inline. >>>>> not savings in text size, I'll settle for the same size. >>>>> ... >>>> It will always be bigger since there are cases where it's unknown at >>>> compile time whether it will be NULL when called. >>> if it's "unknown" you could call into a separate kfree() which does >>> check out of line. (sure that's a dozen bytes bigger but that is >>> noise ;) >> It's noise and _much work. > > not if the compiler can do it. The *compiler* knows a lot (4.1 at > least).. I would think so too. Unfortunately this is what I found for make allyesconfig on 2.6.16.9: text data bss dec hex filename 21615935 7929490 2187672 31733097 1e43569 vmlinux-3.3.5-new 21616824 7929298 2187672 31733794 1e43822 vmlinux-3.3.5-old 21546713 7616546 2184984 31348243 1de5613 vmlinux-4.1.0-new 21546551 7616458 2184984 31347993 1de5519 vmlinux-4.1.0-old Where "old" is the original one, and "new" the one with the included patch applied. So the patch is a small win with gcc-3.3.5 and a small loss on gcc-4.1.0. I don't really understand why 4.1.0 produces larger code with the patch, but I triple-checked... Groeten, Bart -- Bart Hartgers - TUE Eindhoven - http://plasimo.phys.tue.nl/bart/contact/ --------------050403060107080906010809 Content-Type: text/x-patch; name="null-check.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="null-check.patch" --- linux-2.6.16.9/include/linux/slab.h 2006-04-19 08:10:14.000000000 +0200 +++ linux-2.6.16.9-kfree/include/linux/slab.h 2006-04-27 11:19:00.000000000 +0200 @@ -123,7 +123,18 @@ return kzalloc(n * size, flags); } -extern void kfree(const void *); +extern void __kfree(const void *); + +static inline void kfree(const void *ptr) +{ + if (__builtin_constant_p(ptr==NULL)) { + if (ptr) + __kfree(ptr); + } else { + __kfree(ptr); + } +} + extern unsigned int ksize(const void *); #ifdef CONFIG_NUMA --- linux-2.6.16.9/mm/slab.c 2006-04-27 11:24:38.000000000 +0200 +++ linux-2.6.16.9-kfree/mm/slab.c 2006-04-27 11:17:06.000000000 +0200 @@ -3267,7 +3267,7 @@ EXPORT_SYMBOL(kmem_cache_free); /** - * kfree - free previously allocated memory + * __kfree - free previously allocated memory * @objp: pointer returned by kmalloc. * * If @objp is NULL, no operation is performed. @@ -3275,7 +3275,7 @@ * Don't free memory not originally allocated by kmalloc() * or you will run into trouble. */ -void kfree(const void *objp) +void __kfree(const void *objp) { struct kmem_cache *c; unsigned long flags; --------------050403060107080906010809--