From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754113AbcEPPRH (ORCPT ); Mon, 16 May 2016 11:17:07 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:35369 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754050AbcEPPRF (ORCPT ); Mon, 16 May 2016 11:17:05 -0400 Date: Mon, 16 May 2016 17:16:57 +0200 From: Michal Hocko To: Wang Xiaoqiang Cc: vbabka@suse.cz, n-horiguchi@ah.jp.nec.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: Question About Functions "__free_pages_check" and "check_new_page" in page_alloc.c Message-ID: <20160516151657.GC23251@dhcp22.suse.cz> References: <7374bd2e.da35.154b9cda7d2.Coremail.wang_xiaoq@126.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7374bd2e.da35.154b9cda7d2.Coremail.wang_xiaoq@126.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 16-05-16 21:42:23, Wang Xiaoqiang wrote: > Hi all, > > I am really confused about these two functions. The following code snippet: > > if(unlikely(atomic_read(&page->_mapcount) != -1)) > bad_reason ="nonzero mapcount";if(unlikely(page->mapping != NULL)) > bad_reason ="non-NULL mapping";if(unlikely(page_ref_count(page) !=0)) > bad_reason ="nonzero _count"; > ... > Wouldn't the previous value of "bad_reason" be overwritten by > the later? Hope to receive from you. yes it would. Why that would matter. The checks should be in an order which could give us a more specific reason with later checks. bad_page() will then print more detailed information. -- Michal Hocko SUSE Labs