From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id B97DC6B0507 for ; Wed, 12 Jul 2017 07:46:59 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id o105so3205829wrc.5 for ; Wed, 12 Jul 2017 04:46:59 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id h205si2008618wmf.32.2017.07.12.04.46.58 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 12 Jul 2017 04:46:58 -0700 (PDT) Date: Wed, 12 Jul 2017 13:46:55 +0200 From: Michal Hocko Subject: Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing mirroring functionality Message-ID: <20170712114655.GG28912@dhcp22.suse.cz> References: <1499357846-7481-1-git-send-email-mike.kravetz@oracle.com> <1499357846-7481-2-git-send-email-mike.kravetz@oracle.com> <20170711123642.GC11936@dhcp22.suse.cz> <7f14334f-81d1-7698-d694-37278f05a78e@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7f14334f-81d1-7698-d694-37278f05a78e@oracle.com> Sender: owner-linux-mm@kvack.org List-ID: To: Mike Kravetz Cc: linux-mm@kvack.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , Andrea Arcangeli , Aaron Lu , "Kirill A . Shutemov" , Vlastimil Babka On Tue 11-07-17 11:23:19, Mike Kravetz wrote: > On 07/11/2017 05:36 AM, Michal Hocko wrote: [...] > > Anyway the patch should fail with -EINVAL on private mappings as Kirill > > already pointed out > > Yes. I think this should be a separate patch. As mentioned earlier, > mremap today creates a new/additional private mapping if called in this > way with old_size == 0. To me, this is a bug. Not only that. It clears existing ptes in the old mapping so the content is lost. That is quite unexpected behavior. Now it is hard to assume whether somebody relies on the behavior (I can easily imagine somebody doing backup&clear in atomic way) so failing with EINVAL might break userspace so I am not longer sure. Anyway this really needs to be documented. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org