From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f67.google.com ([209.85.218.67]:49451 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752009AbdJTPXD (ORCPT ); Fri, 20 Oct 2017 11:23:03 -0400 Received: by mail-oi0-f67.google.com with SMTP id w197so20555454oif.6 for ; Fri, 20 Oct 2017 08:23:03 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20171020075735.GA14378@lst.de> 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> From: Dan Williams Date: Fri, 20 Oct 2017 08:23:02 -0700 Message-ID: Subject: Re: [PATCH v3 02/13] dax: require 'struct page' for filesystem dax Content-Type: text/plain; charset="UTF-8" Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Christoph Hellwig Cc: 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 12:57 AM, Christoph Hellwig wrote: >> --- a/arch/powerpc/sysdev/axonram.c >> +++ b/arch/powerpc/sysdev/axonram.c >> @@ -172,6 +172,7 @@ static size_t axon_ram_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff, >> >> static const struct dax_operations axon_ram_dax_ops = { >> .direct_access = axon_ram_dax_direct_access, >> + >> .copy_from_iter = axon_ram_copy_from_iter, > > Unrelated whitespace change. That being said - I don't think axonram has > devmap support in any form, so this basically becomes dead code, doesn't > it? > >> diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c >> index 7abb240847c0..e7e5db07e339 100644 >> --- a/drivers/s390/block/dcssblk.c >> +++ b/drivers/s390/block/dcssblk.c >> @@ -52,6 +52,7 @@ static size_t dcssblk_dax_copy_from_iter(struct dax_device *dax_dev, >> >> static const struct dax_operations dcssblk_dax_ops = { >> .direct_access = dcssblk_dax_direct_access, >> + >> .copy_from_iter = dcssblk_dax_copy_from_iter, > > Same comments apply here. Yes, however it seems these drivers / platforms have been living with the lack of struct page for a long time. So they either don't use DAX, or they have a constrained use case that never triggers get_user_pages(). If it is the latter then they could introduce a new configuration option that bypasses the pfn_t_devmap() check in bdev_dax_supported() and fix up the get_user_pages() paths to fail. So, I'd like to understand how these drivers have been using DAX support without struct page to see if we need a workaround or we can go ahead delete this support. If the usage is limited to execute-in-place perhaps we can do a constrained ->direct_access() for just that case.