Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752081AbdGGKX2 (ORCPT ); Fri, 7 Jul 2017 06:23:28 -0400 Received: from mail-wr0-f195.google.com ([209.85.128.195]:33540 "EHLO mail-wr0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751757AbdGGKX1 (ORCPT ); Fri, 7 Jul 2017 06:23:27 -0400 Date: Fri, 7 Jul 2017 13:23:24 +0300 From: "Kirill A. Shutemov" To: Mike Kravetz Cc: linux-mm@kvack.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , Andrea Arcangeli , Michal Hocko , Aaron Lu , "Kirill A . Shutemov" Subject: Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing mirroring functionality Message-ID: <20170707102324.kfihkf72sjcrtn5b@node.shutemov.name> References: <1499357846-7481-1-git-send-email-mike.kravetz@oracle.com> <1499357846-7481-2-git-send-email-mike.kravetz@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1499357846-7481-2-git-send-email-mike.kravetz@oracle.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1062 Lines: 24 On Thu, Jul 06, 2017 at 09:17:26AM -0700, Mike Kravetz wrote: > The mremap system call has the ability to 'mirror' parts of an existing > mapping. To do so, it creates a new mapping that maps the same pages as > the original mapping, just at a different virtual address. This > functionality has existed since at least the 2.6 kernel. > > This patch simply adds a new flag to mremap which will make this > functionality part of the API. It maintains backward compatibility with > the existing way of requesting mirroring (old_size == 0). > > If this new MREMAP_MIRROR flag is specified, then new_size must equal > old_size. In addition, the MREMAP_MAYMOVE flag must be specified. The patch breaks important invariant that anon page can be mapped into a process only once. What is going to happen to mirrored after CoW for instance? In my opinion, it shouldn't be allowed for anon/private mappings at least. And with this limitation, I don't see much sense in the new interface -- just create mirror by mmap()ing the file again. -- Kirill A. Shutemov