From: Jesper Juhl Subject: Re: [PATCH 1/1] fs: Small refactoring of the code in ext4 2.6.37-rc1 Date: Thu, 4 Nov 2010 23:31:58 +0100 (CET) Message-ID: References: <250707.83204.qm@web110504.mail.gq1.yahoo.com> Mime-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="8323328-55086022-1288909876=:16015" Cc: Andreas Dilger , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: =?ISO-8859-15?Q?Andr=E9_Luis_Pereira_dos_Santos_-_BSRSoft?= Return-path: In-Reply-To: <250707.83204.qm@web110504.mail.gq1.yahoo.com> Content-ID: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323328-55086022-1288909876=:16015 Content-Type: TEXT/PLAIN; CHARSET=UTF-8 Content-Transfer-Encoding: 8BIT Content-ID: On Thu, 4 Nov 2010, André Luis Pereira dos Santos - BSRSoft wrote: > From: Andre Luis Pereira dos Santos > > Hi. > Small refactoring of the code in order to make minor enhancements to critical areas. > The notation x + 1 has been replaced by more efficient notation x + +. > > Signed-off-by: Andre Luis Pereira dos Santos > --- > Signed-off-by: Andre Luis Pereira dos Santos > --- linux-2.6.37-rc1/fs/ext4/extents.c 2010-11-01 09:54:12.000000000 -0200 > +++ linux-2.6.37-rc1-patched/fs/ext4/extents.c 2010-11-04 19:54:26.000000000 -0200 > @@ -555,9 +555,9 @@ ext4_ext_binsearch(struct inode *inode, > while (l <= r) { > m = l + (r - l) / 2; > if (block < le32_to_cpu(m->ee_block)) > - r = m - 1; > + r = m--; > else > - l = m + 1; > + l = m++; These do not give identical results. foo = bar + 1; assigns (bar + 1) to foo. foo = bar--; assigns bar to foo then decrements bar. foo = --bar; decrements bar then assigns bar to foo. So your change both change the value that will be assigned to 'r' and 'l' and also modify 'm' which was not previously modified. > ext_debug("%p(%u):%p(%u):%p(%u) ", l, le32_to_cpu(l->ee_block), > m, le32_to_cpu(m->ee_block), > r, le32_to_cpu(r->ee_block)); > @@ -1557,7 +1557,7 @@ static int ext4_ext_try_to_merge(struct > if (ext4_ext_is_uninitialized(ex)) > uninitialized = 1; > ex->ee_len = cpu_to_le16(ext4_ext_get_actual_len(ex) > - + ext4_ext_get_actual_len(ex + 1)); > + + ext4_ext_get_actual_len(ex++)); After your change gcc complains: fs/ext4/extents.c:1559:16: warning: operation on ‘ex’ may be undefined fs/ext4/extents.c:1559:16: warning: operation on ‘ex’ may be undefined which it is correct in doing since you are now modifying the value of the pointer which is dereferenced in the assignment. Previously the value of (ex+1) was simply passed to ext4_ext_get_actual_len(), but now you are passing the value of (ex) to ext4_ext_get_actual_len() and then subsequently incrementing 'ex' itself. > if (uninitialized) > ext4_ext_mark_uninitialized(ex); > > Was this patch even compile tested? -- Jesper Juhl http://www.chaosbits.net/ Plain text mails only, please http://www.expita.com/nomime.html Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html --8323328-55086022-1288909876=:16015--