From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751543AbbIJWcm (ORCPT ); Thu, 10 Sep 2015 18:32:42 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:47136 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750764AbbIJWcl (ORCPT ); Thu, 10 Sep 2015 18:32:41 -0400 Date: Thu, 10 Sep 2015 15:32:40 -0700 From: Andrew Morton To: gang.chen.5i5j@gmail.com Cc: mhocko@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, gchen_5i5j@21cn.com Subject: Re: [PATCH] mm/mmap.c: Remove redundent 'get_area' function pointer in get_unmapped_area() Message-Id: <20150910153240.9572375a7a5359a6e2a7ab4a@linux-foundation.org> In-Reply-To: <1441253691-5798-1-git-send-email-gang.chen.5i5j@gmail.com> References: <1441253691-5798-1-git-send-email-gang.chen.5i5j@gmail.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 3 Sep 2015 12:14:51 +0800 gang.chen.5i5j@gmail.com wrote: > From: Chen Gang > > Call the function pointer directly, then let code a bit simpler. > > ... > > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2012,10 +2012,8 @@ unsigned long > get_unmapped_area(struct file *file, unsigned long addr, unsigned long len, > unsigned long pgoff, unsigned long flags) > { > - unsigned long (*get_area)(struct file *, unsigned long, > - unsigned long, unsigned long, unsigned long); > - > unsigned long error = arch_mmap_check(addr, len, flags); > + > if (error) > return error; > > @@ -2023,10 +2021,12 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len, > if (len > TASK_SIZE) > return -ENOMEM; > > - get_area = current->mm->get_unmapped_area; > if (file && file->f_op->get_unmapped_area) > - get_area = file->f_op->get_unmapped_area; > - addr = get_area(file, addr, len, pgoff, flags); > + addr = file->f_op->get_unmapped_area(file, addr, len, > + pgoff, flags); > + else > + addr = current->mm->get_unmapped_area(file, addr, len, > + pgoff, flags); > if (IS_ERR_VALUE(addr)) > return addr; size(1) says this generates more object code. And that probably means slightly worse code. I didn't investigate, but probably the compiler is now preparing those five args at two different sites. Which is pretty dumb of it - the compiler could have stacked the args first, then chosen the appropriate function to call.