From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id C8DC86B0253 for ; Mon, 25 Sep 2017 08:40:47 -0400 (EDT) Received: by mail-oi0-f71.google.com with SMTP id r20so7870846oie.0 for ; Mon, 25 Sep 2017 05:40:47 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id x131si3555238oix.525.2017.09.25.05.40.46 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Sep 2017 05:40:46 -0700 (PDT) Subject: Re: [patch] mremap.2: Add description of old_size == 0 functionality References: <20170915213745.6821-1-mike.kravetz@oracle.com> <20170925123508.pzjbe7wgwagnr5li@dhcp22.suse.cz> From: Florian Weimer Message-ID: Date: Mon, 25 Sep 2017 14:40:42 +0200 MIME-Version: 1.0 In-Reply-To: <20170925123508.pzjbe7wgwagnr5li@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Mike Kravetz , mtk.manpages@gmail.com, linux-man@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Andrea Arcangeli , "Kirill A . Shutemov" , Vlastimil Babka , Anshuman Khandual , linux-mm@kvack.org On 09/25/2017 02:35 PM, Michal Hocko wrote: > What would be the usecase. I mean why don't you simply create a new > mapping by a plain mmap when you have no guarantee about the same > content? I plan to use it for creating an unbounded number of callback thunks at run time, from a single set of pages in libc.so, in case we need this functionality. The idea is to duplicate existing position-independent machine code in libc.so, prefixed by a data mapping which controls its behavior. Each data/code combination would only give us a fixed number of thunks, so we'd need to create a new mapping to increase the total number. Instead, we could re-map the code from the executable in disk, but not if chroot has been called or glibc has been updated on disk. Creating an alias mapping does not have these problems. Another application (but that's for anonymous memory) would be to duplicate class metadata in a Java-style VM, so that you can use bits in the class pointer in each Java object (which is similar to the vtable pointer in C++) for the garbage collector, without having to mask it when accessing the class metadata in regular (mutator) code. Thanks, Florian -- 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