From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755512Ab0E2N1N (ORCPT ); Sat, 29 May 2010 09:27:13 -0400 Received: from mail-px0-f174.google.com ([209.85.212.174]:57565 "EHLO mail-px0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752929Ab0E2N1I convert rfc822-to-8bit (ORCPT ); Sat, 29 May 2010 09:27:08 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :content-type:content-transfer-encoding; b=AaPLIqgAnsluwlAMuADcIxsRgPV2aaj3H7O23Zwvor2sWD9/WcFnohrNltvB5OFRCU sQ0P8YUWiFBLWQ0hDG146rtLXR/I5b8VoK4gPfbn94Sj7H+TCzRFLxQhd4WZmCE/CWYi i0ZvDjwY2X2wuyZRPkF/ApAY4LyrVpzR9dWr8= MIME-Version: 1.0 In-Reply-To: <20100529121019.GA25092@liondog.tnic> References: <1275095926-18345-1-git-send-email-xiaosuo@gmail.com> <20100529121019.GA25092@liondog.tnic> From: Changli Gao Date: Sat, 29 May 2010 21:26:47 +0800 Message-ID: Subject: Re: [PATCH 1/2] fs: optimize mpage_readpage() To: Borislav Petkov , Changli Gao , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 29, 2010 at 8:10 PM, Borislav Petkov wrote: > From: Changli Gao > Date: Sat, May 29, 2010 at 09:18:46AM +0800 > >> optimize mpage_readpage() >> >> we don't need to initialize bio, and pass it to do_mpage_readpage() as >> parameter, as it is returned by do_mpage_readpage(). >> >> Signed-off-by: Changli Gao >> ---- >>  fs/mpage.c |    4 ++-- >>  1 file changed, 2 insertions(+), 2 deletions(-) >> diff --git a/fs/mpage.c b/fs/mpage.c >> index fd56ca2..94ff0d1 100644 >> --- a/fs/mpage.c >> +++ b/fs/mpage.c >> @@ -409,14 +409,14 @@ EXPORT_SYMBOL(mpage_readpages); >>   */ >>  int mpage_readpage(struct page *page, get_block_t get_block) >>  { >> -     struct bio *bio = NULL; >> +     struct bio *bio; >>       sector_t last_block_in_bio = 0; >>       struct buffer_head map_bh; >>       unsigned long first_logical_block = 0; >> >>       map_bh.b_state = 0; >>       map_bh.b_size = 0; >> -     bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio, >> +     bio = do_mpage_readpage(NULL, page, 1, &last_block_in_bio, >>                       &map_bh, &first_logical_block, get_block); >>       if (bio) >>               mpage_bio_submit(READ, bio); > > Nope, I don't think that's a good idea. > > On the one hand, this is a trick to shut up gcc: > > fs/mpage.c: In function ‘mpage_readpage’: > fs/mpage.c:419: warning: ‘bio’ is used uninitialized in this function > > and, on the other hand, make sure bio is NULL and not some random stack > value since bio is explicitly checked for NULL in do_mpage_readpage(). > Did the compiler warning appear after applying my patch? It doesn't happen when I testing it. And I don't pass bio to do_mpage_readpage(), but I pass NULL instead. -- Regards， Changli Gao(xiaosuo@gmail.com)