From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f72.google.com (mail-oi0-f72.google.com [209.85.218.72]) by kanga.kvack.org (Postfix) with ESMTP id 2C70A6B0038 for ; Thu, 15 Sep 2016 13:10:07 -0400 (EDT) Received: by mail-oi0-f72.google.com with SMTP id x203so6260754oia.3 for ; Thu, 15 Sep 2016 10:10:07 -0700 (PDT) Received: from aserp1040.oracle.com (aserp1040.oracle.com. [141.146.126.69]) by mx.google.com with ESMTPS id n4si4812379itg.125.2016.09.15.10.09.48 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 15 Sep 2016 10:09:48 -0700 (PDT) Date: Thu, 15 Sep 2016 10:09:42 -0700 From: "Darrick J. Wong" Subject: Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Message-ID: <20160915170942.GJ9314@birch.djwong.org> References: <147392246509.9873.17750323049785100997.stgit@dwillia2-desk3.amr.corp.intel.com> <147392247875.9873.4205533916442000884.stgit@dwillia2-desk3.amr.corp.intel.com> <20160915082615.GA9772@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams Cc: Christoph Hellwig , "linux-nvdimm@lists.01.org" , "linux-kernel@vger.kernel.org" , Nicholas Piggin , XFS Developers , Linux MM , linux-fsdevel On Thu, Sep 15, 2016 at 10:01:03AM -0700, Dan Williams wrote: > On Thu, Sep 15, 2016 at 1:26 AM, Christoph Hellwig wrote: > > On Wed, Sep 14, 2016 at 11:54:38PM -0700, Dan Williams wrote: > >> The DAX property, page cache bypass, of a VMA is only detectable via the > >> vma_is_dax() helper to check the S_DAX inode flag. However, this is > >> only available internal to the kernel and is a property that userspace > >> applications would like to interrogate. > > > > They have absolutely no business knowing such an implementation detail. > > Hasn't that train already left the station with FS_XFLAG_DAX? Seeing as FS_IOC_FSGETXATTR is a "generic" ioctl now, why not just implement it for all the DAX fses and block devices? Aside from xflags, the other fields are probably all zero for non-xfs (aside from project quota id I guess). (Yeah, sort of awkward, I know...) --D > The other problem with hiding the DAX property is that it turns out to > not be a transparent acceleration feature. See xfs/086 xfs/088 > xfs/089 xfs/091 which fail with DAX and, as far as I understand, it is > due to the fact that DAX disallows delayed allocation behavior. > > If behavior changes I think we should indicate that to userspace and > VM_DAX is certainly more useful to userspace than some of the other vm > internals we already export in those flags. > > _______________________________________________ > xfs mailing list > xfs@oss.sgi.com > http://oss.sgi.com/mailman/listinfo/xfs -- 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