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 17ADF6B049E for ; Fri, 25 Aug 2017 16:24:33 -0400 (EDT) Received: by mail-oi0-f71.google.com with SMTP id d66so760479oib.2 for ; Fri, 25 Aug 2017 13:24:33 -0700 (PDT) Received: from mail-oi0-x232.google.com (mail-oi0-x232.google.com. [2607:f8b0:4003:c06::232]) by mx.google.com with ESMTPS id j186si6212354oia.7.2017.08.25.13.24.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 25 Aug 2017 13:24:32 -0700 (PDT) Received: by mail-oi0-x232.google.com with SMTP id r9so7592737oie.3 for ; Fri, 25 Aug 2017 13:24:31 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <4de21e8d-5e10-ec40-c731-0c079953cf48@gmx.de> References: <150353211413.5039.5228914877418362329.stgit@dwillia2-desk3.amr.corp.intel.com> <150353213097.5039.6729469069608762658.stgit@dwillia2-desk3.amr.corp.intel.com> <20170824165546.GA3121@infradead.org> <20170825130011.GA30072@infradead.org> <20170825155803.4km7wttzadfqw2vb@node.shutemov.name> <20170825160236.GA2561@infradead.org> <20170825161607.6v6beg4zjktllt2z@node.shutemov.name> <4de21e8d-5e10-ec40-c731-0c079953cf48@gmx.de> From: Dan Williams Date: Fri, 25 Aug 2017 13:24:31 -0700 Message-ID: Subject: Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap flags Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Helge Deller Cc: "Kirill A. Shutemov" , Christoph Hellwig , Andrew Morton , Jan Kara , Arnd Bergmann , "linux-nvdimm@lists.01.org" , Linux API , "linux-kernel@vger.kernel.org" , linux-xfs@vger.kernel.org, Linux MM , Andy Lutomirski , linux-fsdevel , "Kirill A. Shutemov" , linux-parisc@vger.kernel.org On Fri, Aug 25, 2017 at 9:19 AM, Helge Deller wrote: > On 25.08.2017 18:16, Kirill A. Shutemov wrote: >> On Fri, Aug 25, 2017 at 09:02:36AM -0700, Christoph Hellwig wrote: >>> On Fri, Aug 25, 2017 at 06:58:03PM +0300, Kirill A. Shutemov wrote: >>>> Not all archs are ready for this: >>>> >>>> arch/parisc/include/uapi/asm/mman.h:#define MAP_TYPE 0x03 /* Mask for type of mapping */ >>>> arch/parisc/include/uapi/asm/mman.h:#define MAP_FIXED 0x04 /* Interpret addr exactly */ >>> >>> I'd be happy to say that we should not care about parisc for >>> persistent memory. We'll just have to find a way to exclude >>> parisc without making life too ugly. >> >> I don't think creapling mmap() interface for one arch is the right way to >> go. I think the interface should be universal. >> >> I may imagine MAP_DIRECT can be useful not only for persistent memory. >> For tmpfs instead of mlock()? > > On parisc we have > #define MAP_SHARED 0x01 /* Share changes */ > #define MAP_PRIVATE 0x02 /* Changes are private */ > #define MAP_TYPE 0x03 /* Mask for type of mapping */ > #define MAP_FIXED 0x04 /* Interpret addr exactly */ > #define MAP_ANONYMOUS 0x10 /* don't use a file */ > > So, if you need a MAP_DIRECT, wouldn't e.g. > #define MAP_DIRECT 0x08 > be possible (for parisc, and others 0x04). > And if MAP_TYPE needs to include this flag on parisc: > #define MAP_TYPE (0x03 | 0x08) /* Mask for type of mapping */ The problem here is that to support new the mmap flags the arch needs to find a flag that is guaranteed to fail on older kernels. Defining MAP_DIRECT to 0x8 on parisc doesn't work because it will simply be ignored on older parisc kernels. However, it's already the case that several archs have their own sys_mmap entry points. Those archs that can't follow the common scheme (only parsic it seems) will need to add a new mmap syscall. I think that's a reasonable tradeoff to allow every other architecture to add this support with their existing mmap syscall paths. That means MAP_DIRECT should be defined to MAP_TYPE on parisc until it later defines an opt-in mechanism to a new syscall that honors MAP_DIRECT as a valid flag. -- 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