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 23DC16B0038 for ; Sat, 21 Oct 2017 00:16:24 -0400 (EDT) Received: by mail-oi0-f72.google.com with SMTP id 14so13070517oii.2 for ; Fri, 20 Oct 2017 21:16:24 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id k13sor996648oih.294.2017.10.20.21.16.23 for (Google Transport Security); Fri, 20 Oct 2017 21:16:23 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20171021032008.GA27694@bombadil.infradead.org> References: <150846713528.24336.4459262264611579791.stgit@dwillia2-desk3.amr.corp.intel.com> <150846714747.24336.14704246566580871364.stgit@dwillia2-desk3.amr.corp.intel.com> <20171020075735.GA14378@lst.de> <20171020162933.GA26320@lst.de> <20171021032008.GA27694@bombadil.infradead.org> From: Dan Williams Date: Fri, 20 Oct 2017 21:16:21 -0700 Message-ID: Subject: Re: [PATCH v3 02/13] dax: require 'struct page' for filesystem dax Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Christoph Hellwig , Andrew Morton , Jan Kara , "linux-nvdimm@lists.01.org" , Benjamin Herrenschmidt , Heiko Carstens , "linux-kernel@vger.kernel.org" , linux-xfs@vger.kernel.org, Linux MM , Jeff Moyer , Paul Mackerras , Michael Ellerman , Martin Schwidefsky , linux-fsdevel , Ross Zwisler , Gerald Schaefer On Fri, Oct 20, 2017 at 8:20 PM, Matthew Wilcox wrote: > On Fri, Oct 20, 2017 at 03:29:57PM -0700, Dan Williams wrote: >> Ok, I'd also like to kill DAX support in the brd driver. It's a source >> of complexity and maintenance burden for zero benefit. It's the only >> ->direct_access() implementation that sleeps and it's the only >> implementation where there is a non-linear relationship between >> sectors and pfns. Having a 1:1 sector to pfn relationship will help >> with the dma-extent-busy management since we don't need to keep >> calling into the driver to map pfns back to sectors once we know the >> pfn[0] sector[0] relationship. > > But these are important things that other block devices may / will want. > > For example, I think it's entirely sensible to support ->direct_access > for RAID-0. Dell are looking at various different options for having > one pmemX device per DIMM and using RAID to lash them together. > ->direct_access makes no sense for RAID-5 or RAID-1, but RAID-0 makes > sense to me. > > Last time we tried to take sleeping out, there were grumblings from people > with network block devices who thought they'd want to bring pages in > across the network. I'm a bit less sympathetic to this because I don't > know anyone actively working on it, but the RAID-0 case is something I > think we should care about. True, good point. In fact we already support device-mapper striping with ->direct_access(). I'd still like to go ahead with the sleeping removal. When those folks come back and add network direct_access they can do the hard work of figuring out cases where we need to call direct_access in atomic contexts. -- 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