Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753312Ab3FJLHV (ORCPT ); Mon, 10 Jun 2013 07:07:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37033 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752500Ab3FJLHU (ORCPT ); Mon, 10 Jun 2013 07:07:20 -0400 Subject: Re: [PATCH] GFS2: minor readability improvement in gfs2_mount() From: Steven Whitehouse To: Alexey Khoroshilov Cc: cluster-devel@redhat.com, linux-kernel@vger.kernel.org, ldv-project@linuxtesting.org In-Reply-To: <51B1828E.6060301@ispras.ru> References: <1370467772-4587-1-git-send-email-khoroshilov@ispras.ru> <1370510682.2744.5.camel@menhir> <51B1828E.6060301@ispras.ru> Content-Type: text/plain; charset="UTF-8" Organization: Red Hat UK Ltd Date: Mon, 10 Jun 2013 12:04:44 +0100 Message-ID: <1370862284.2715.36.camel@menhir> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2652 Lines: 68 Hi, On Fri, 2013-06-07 at 10:49 +0400, Alexey Khoroshilov wrote: > Hi Steve, > > On 06/06/2013 01:24 PM, Steven Whitehouse wrote: > > Hi, > > > > On Thu, 2013-06-06 at 01:29 +0400, Alexey Khoroshilov wrote: > >> The patch makes usage pattern of IS_ERR-PTR_ERR more typical. > >> > >> Signed-off-by: Alexey Khoroshilov > >> --- > >> fs/gfs2/ops_fstype.c | 5 +++-- > >> 1 file changed, 3 insertions(+), 2 deletions(-) > >> > >> diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c > >> index 0262c19..0d30e8e 100644 > >> --- a/fs/gfs2/ops_fstype.c > >> +++ b/fs/gfs2/ops_fstype.c > >> @@ -1313,9 +1313,10 @@ static struct dentry *gfs2_mount(struct file_system_type *fs_type, int flags, > >> } > >> s = sget(fs_type, test_gfs2_super, set_gfs2_super, flags, bdev); > >> mutex_unlock(&bdev->bd_fsfreeze_mutex); > >> - error = PTR_ERR(s); > >> - if (IS_ERR(s)) > >> + if (IS_ERR(s)) { > >> + error = PTR_ERR(s); > >> goto error_bdev; > >> + } > > I'm not sure what you are getting at here. Why add a jump into the fast > > path? > My experiments with gcc 4.7.3 on x86-64 do not show any difference in > code generated with patch and without it. > 227a: e8 00 00 00 00 callq 227f > 227b: R_X86_64_PC32 sget-0x4 > 227f: 4c 89 f7 mov %r14,%rdi > 2282: 49 89 c4 mov %rax,%r12 > 2285: e8 00 00 00 00 callq 228a > 2286: R_X86_64_PC32 mutex_unlock-0x4 > 228a: 49 81 fc 00 f0 ff ff cmp $0xfffffffffffff000,%r12 > 2291: 0f 87 2a 01 00 00 ja 23c1 > 2297: 49 83 7c 24 60 00 cmpq $0x0,0x60(%r12) > 229d: 74 0b je 22aa > 229f: 44 89 ee mov %r13d,%esi > 22a2: 48 89 df mov %rbx,%rdi > 22a5: e8 00 00 00 00 callq 22aa > 22a6: R_X86_64_PC32 blkdev_put-0x4 > > It looks like 'error = PTR_ERR(s);' assignment is just ignored because s and error share the same register %r12. > > So the only point of the patch is to improve readability. > Hmm, ok. I'm still not convinced that it does really improve readability in this case I'm afraid, so I'm not going to apply this one, Steve. > -- > Best regards, > Alexey -- 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/