From: Dan Williams Subject: Re: [RFC PATCH 0/7] dax, ext4: Synchronous page faults Date: Sun, 13 Aug 2017 10:08:41 -0700 Message-ID: References: <20170727131245.28279-1-jack@suse.cz> <20170727215713.GA22000@linux.intel.com> <20170728093821.GB29433@quack2.suse.cz> <20170801110241.GE6742@infradead.org> <20170801112603.GG4215@quack2.suse.cz> <20170811100327.GD7064@infradead.org> <20170813092556.GA19019@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: linux-xfs@vger.kernel.org, Jan Kara , linux-nvdimm , Dave Chinner , Andy Lutomirski , Linux FS Devel , "linux-ext4@vger.kernel.org" To: Christoph Hellwig Return-path: Received: from mail-wm0-f67.google.com ([74.125.82.67]:38597 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751000AbdHMRIo (ORCPT ); Sun, 13 Aug 2017 13:08:44 -0400 In-Reply-To: <20170813092556.GA19019@infradead.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Sun, Aug 13, 2017 at 2:25 AM, Christoph Hellwig wrote: > On Sat, Aug 12, 2017 at 07:44:14PM -0700, Dan Williams wrote: >> How about MAP_SYNC == (MAP_SHARED|MAP_PRIVATE)? On older kernels that >> should get -EINVAL, and on new kernels it means SYNC+SHARED. > > Cute trick, but I'd hate to waster it just for our little flag. > > How about: > > #define __MAP_VALIDATE MAP_SHARED|MAP_PRIVATE > #define MAP_SYNC 0x??? | __MAP_VALIDATE > > so that we can reuse that trick for any new flag? Yes, even better. I think that effectively kicks the need for mmap3() down the road a bit.