From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751679AbeCOM3s (ORCPT ); Thu, 15 Mar 2018 08:29:48 -0400 Received: from mx2.suse.de ([195.135.220.15]:37003 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751556AbeCOM3r (ORCPT ); Thu, 15 Mar 2018 08:29:47 -0400 Date: Thu, 15 Mar 2018 13:29:44 +0100 From: Michal Hocko To: Zi Yan Cc: "Huang, Ying" , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , Minchan Kim , Shaohua Li , jglisse@redhat.com, "Aneesh Kumar K.V" Subject: Re: [PATCH -mm] mm, madvise, THP: Use THP aligned address in madvise_free_huge_pmd() Message-ID: <20180315122944.GH23100@dhcp22.suse.cz> References: <20180315011840.27599-1-ying.huang@intel.com> <869F4AAA-5BBA-40D6-916F-6919E515D271@cs.rutgers.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <869F4AAA-5BBA-40D6-916F-6919E515D271@cs.rutgers.edu> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 14-03-18 21:39:54, Zi Yan wrote: > This cannot happen. > > Two address parameters are passed: addr and next. > If “addr” is not aligned and “next” is aligned or the end of madvise range, which might not be aligned, > either way next - addr < HPAGE_PMD_SIZE. > > This means the code in “if (next - addr != HPAGE_PMD_SIZE)”, which is above your second hunk, > will split the THP between “addr” and “next” and get out as long as “addr“ is not aligned. > Thus, the code in your second hunk should always get aligned “addr”. OK, so what would happen if the above doesn't hold anymore after some change up the call chain? Is it critical? If yes, do we want VM_BUG_ON to detect that? Or at least document the asumption? -- Michal Hocko SUSE Labs