From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95DBCCA9EC4 for ; Tue, 29 Oct 2019 07:08:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6232D20862 for ; Tue, 29 Oct 2019 07:08:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6232D20862 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id EDF266B0005; Tue, 29 Oct 2019 03:08:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E90CC6B0006; Tue, 29 Oct 2019 03:08:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DA51B6B0007; Tue, 29 Oct 2019 03:08:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0096.hostedemail.com [216.40.44.96]) by kanga.kvack.org (Postfix) with ESMTP id B24096B0005 for ; Tue, 29 Oct 2019 03:08:44 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 49CA9181AF5D3 for ; Tue, 29 Oct 2019 07:08:44 +0000 (UTC) X-FDA: 76095944568.23.berry15_86735058a1755 X-HE-Tag: berry15_86735058a1755 X-Filterd-Recvd-Size: 2484 Received: from gentwo.org (gentwo.org [3.19.106.255]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Tue, 29 Oct 2019 07:08:43 +0000 (UTC) Received: by gentwo.org (Postfix, from userid 1002) id D5B1F3EF13; Tue, 29 Oct 2019 07:08:42 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by gentwo.org (Postfix) with ESMTP id D4C183EA21; Tue, 29 Oct 2019 07:08:42 +0000 (UTC) Date: Tue, 29 Oct 2019 07:08:42 +0000 (UTC) From: Christopher Lameter X-X-Sender: cl@www.lameter.com To: "Kirill A. Shutemov" cc: Mike Rapoport , linux-kernel@vger.kernel.org, Alexey Dobriyan , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Dave Hansen , James Bottomley , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , linux-api@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, Mike Rapoport Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings In-Reply-To: <20191028131623.zwuwguhm4v4s5imh@box> Message-ID: References: <1572171452-7958-1-git-send-email-rppt@kernel.org> <1572171452-7958-2-git-send-email-rppt@kernel.org> <20191028123124.ogkk5ogjlamvwc2s@box> <20191028130018.GA7192@rapoport-lnx> <20191028131623.zwuwguhm4v4s5imh@box> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 28 Oct 2019, Kirill A. Shutemov wrote: > Setting a single 4k page non-present in the direct mapping will require > splitting 2M or 1G page we usually map direct mapping with. And it's one > way road. We don't have any mechanism to map the memory with huge page > again after the application has freed the page. > > It might be okay if all these pages cluster together, but I don't think we > have a way to achieve it easily. Set aside a special physical memory range for this and migrate the page to that physical memory range when MAP_EXCLUSIVE is specified? Maybe some processors also have hardware ranges that offer additional protection for stuff like that?