From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:44342 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752716AbeAaRsm (ORCPT ); Wed, 31 Jan 2018 12:48:42 -0500 Date: Wed, 31 Jan 2018 12:48:40 -0500 From: Jerome Glisse To: Igor Stoppa Cc: lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org Subject: Re: [LSF/MM TOPIC] Killing reliance on struct page->mapping Message-ID: <20180131174840.GF2912@redhat.com> References: <20180130004347.GD4526@redhat.com> <111f49c1-02d1-3355-e403-a8f91c0191e2@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 In-Reply-To: <111f49c1-02d1-3355-e403-a8f91c0191e2@huawei.com> Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On Wed, Jan 31, 2018 at 07:09:48PM +0200, Igor Stoppa wrote: > On 30/01/18 02:43, Jerome Glisse wrote: > > [...] > > > Maybe we can kill page->mapping altogether as a result of this. However this is > > not my motivation at this time. > > We had a discussion some time ago > > http://www.openwall.com/lists/kernel-hardening/2017/07/07/7 > > where you advised to use it for tracking pmalloc pages vs area, which > generated this patch: > > http://www.openwall.com/lists/kernel-hardening/2018/01/24/7 > > Could you please comment what wold happen to the shortcut from struct > page to vm_struct that this patch is now introducing? Sadly struct page fields means different thing depending on the context in which the page is use. This is confusing i know. So when i say kill page->mapping i am not saying shrink the struct page and remove that field, i am saying maybe we can kill current user of page->mapping for regular process page (ie page that are in some mmap() area of a process). Other use of that field in different context like yours are not affected by this change and can ignore it alltogether. Hope this clarify it :) Cheers, J�r�me