Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751776AbZGTDHA (ORCPT ); Sun, 19 Jul 2009 23:07:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751439AbZGTDHA (ORCPT ); Sun, 19 Jul 2009 23:07:00 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:54611 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751042AbZGTDG7 (ORCPT ); Sun, 19 Jul 2009 23:06:59 -0400 Message-ID: <4A63DF71.2070905@cn.fujitsu.com> Date: Mon, 20 Jul 2009 11:07:29 +0800 From: Zhaolei User-Agent: Thunderbird 2.0.0.6 (Windows/20070728) MIME-Version: 1.0 To: Ingo Molnar , David Rientjes CC: Thomas Gleixner , "H. Peter Anvin" , Vegard Nossum , linux-kernel@vger.kernel.org Subject: Re: Re: [PATCH] Remove initialization of page_table in one_page_table_init() References: <4A5C488A.90204@cn.fujitsu.com> <20090718141157.GH32618@elte.hu> In-Reply-To: <20090718141157.GH32618@elte.hu> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1905 Lines: 56 Ingo Molnar wrote: > * Zhaolei wrote: > >> Only judge if (!page_table) when CONFIG_DEBUG_PAGEALLOC or CONFIG_KMEMCHECK >> are defined, then we don't need to set init value for page_table. >> >> Signed-off-by: Zhao Lei >> --- >> arch/x86/mm/init_32.c | 4 ++-- >> 1 files changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c >> index 3cd7711..55da09b 100644 >> --- a/arch/x86/mm/init_32.c >> +++ b/arch/x86/mm/init_32.c >> @@ -108,13 +108,13 @@ static pmd_t * __init one_md_table_init(pgd_t *pgd) >> static pte_t * __init one_page_table_init(pmd_t *pmd) >> { >> if (!(pmd_val(*pmd) & _PAGE_PRESENT)) { >> - pte_t *page_table = NULL; >> + pte_t *page_table; >> >> if (after_bootmem) { >> #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KMEMCHECK) >> page_table = (pte_t *) alloc_bootmem_pages(PAGE_SIZE); >> -#endif >> if (!page_table) >> +#endif >> page_table = >> (pte_t *)alloc_bootmem_low_pages(PAGE_SIZE); > > I think the original code was cleaner - putting an #ifdef straight > into the middle of a control block is quite fragile. > > Ingo > Hello, Ingo David Rientjes said that: Nack, gcc will already optimize the branch out for configs without CONFIG_DEBUG_PAGEALLOC and CONFIG_KMEMCHECK. The only thing this change does is make the code less readable. I tested it with gcc -O2, and proved that David is correct. Initialization of page_table and additional "if (!page_table)" was removed by optimization. Please ignore this patch. Thanks Zhaolei -- 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/