From: "Mike Snitzer" Subject: why unlikely(rsv) in ext3_clear_inode()? Date: Mon, 27 Oct 2008 18:29:10 -0400 Message-ID: <170fa0d20810271529g3c64ae89me29ed8b65a9c3b5e@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Andrew Morton" , "Steven Rostedt" To: linux-ext4@vger.kernel.org Return-path: Received: from ey-out-2122.google.com ([74.125.78.26]:23835 "EHLO ey-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751861AbYJ0W3N (ORCPT ); Mon, 27 Oct 2008 18:29:13 -0400 Received: by ey-out-2122.google.com with SMTP id 6so919605eyi.37 for ; Mon, 27 Oct 2008 15:29:11 -0700 (PDT) Content-Disposition: inline Sender: linux-ext4-owner@vger.kernel.org List-ID: Please see: e6022603b9aa7d61d20b392e69edcdbbc1789969 Having a look at the LKML archives this was raised back in 2006: http://lkml.org/lkml/2006/6/23/337 I'm not interested in whether unlikely() actually helps here. I'm still missing _why_ rsv is mostly NULL at this callsite, as Andrew asserted here: http://lkml.org/lkml/2006/6/23/400 And then Steve here: http://lkml.org/lkml/2006/6/24/76 Where he said: "The problem is that in these cases the pointer is NULL several thousands of times for every time it is not NULL (if ever). The non-NULL case is where an error occurred or something very special. So I don't see how the if here is a problem?" I'm missing which error or what "something very special" is the unlikely() reason for having rsv be NULL. Looking at the code; ext3_clear_inode() is _the_ place where the i_block_alloc_info is cleaned up. In my testing the rsv is _never_ NULL if the file was open for writing. Are we saying that reads are much more common than writes? May be a reasonable assumption but saying as much is very different than what Steve seemed to be eluding to... Anyway, I'd appreciate some clarification here. thanks, Mike