Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765696AbXHQShl (ORCPT ); Fri, 17 Aug 2007 14:37:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752534AbXHQSh1 (ORCPT ); Fri, 17 Aug 2007 14:37:27 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:52547 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1765431AbXHQShZ (ORCPT ); Fri, 17 Aug 2007 14:37:25 -0400 Date: Sat, 18 Aug 2007 00:20:09 +0530 (IST) From: Satyam Sharma X-X-Sender: satyam@enigma.security.iitk.ac.in To: Arjan van de Ven cc: Andrew Morton , Tim Bird , linux kernel , Christoph Lameter Subject: Re: kfree(0) - ok? In-Reply-To: <1187375514.2615.0.camel@laptopd505.fenrus.org> Message-ID: References: <46C233CB.9000602@am.sony.com> <1187132149.2618.2.camel@laptopd505.fenrus.org> <20070817112253.e6a7cb33.akpm@linux-foundation.org> <1187375514.2615.0.camel@laptopd505.fenrus.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1446 Lines: 39 On Fri, 17 Aug 2007, Arjan van de Ven wrote: > > On Fri, 2007-08-17 at 11:22 -0700, Andrew Morton wrote: > > On Wed, 15 Aug 2007 05:12:41 +0530 (IST) > > Satyam Sharma wrote: > > > > > [PATCH] {slub, slob}: use unlikely() for kfree(ZERO_OR_NULL_PTR) check > > > > > > Considering kfree(NULL) would normally occur only in error paths and > > > kfree(ZERO_SIZE_PTR) is uncommon as well, so let's use unlikely() for > > > the condition check in SLUB's and SLOB's kfree() to optimize for the > > > common case. SLAB has this already. > > > > I went through my current versions of slab/slub/slub and came up with this: > > > > diff -puN mm/slob.c~slub-slob-use-unlikely-for-kfreezero_or_null_ptr-check mm/slob.c > > --- a/mm/slob.c~slub-slob-use-unlikely-for-kfreezero_or_null_ptr-check > > +++ a/mm/slob.c > > @@ -360,7 +360,7 @@ static void slob_free(void *block, int s > > slobidx_t units; > > unsigned long flags; > > > > - if (ZERO_OR_NULL_PTR(block)) > > + if (unlikely(ZERO_OR_NULL_PTR(block))) > > > > btw this makes NO sense at all; gcc already defaults to assuming > unlikely if you check a pointer for NULL.... ZERO_OR_NULL_PTR() is not a check for NULL. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/