Received-SPF: pass (google.com: best guess record for domain of linux-ext4-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190510155202.14737-1-pagupta@redhat.com> <20190510155202.14737-4-pagupta@redhat.com>
In-Reply-To: <20190510155202.14737-4-pagupta@redhat.com>
From:   Dan Williams <dan.j.williams@intel.com>
Date:   Fri, 10 May 2019 13:14:07 -0700
Message-ID: <CAPcyv4hbVNRFSyS2CTbmO88uhnbeH4eiukAng2cxgbDzLfizwg@mail.gmail.com>
Subject: Re: [PATCH v8 3/6] libnvdimm: add dax_dev sync flag
To:     Pankaj Gupta <pagupta@redhat.com>
Cc:     linux-nvdimm <linux-nvdimm@lists.01.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        virtualization@lists.linux-foundation.org,
        KVM list <kvm@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux ACPI <linux-acpi@vger.kernel.org>,
        Qemu Developers <qemu-devel@nongnu.org>,
        linux-ext4 <linux-ext4@vger.kernel.org>,
        linux-xfs <linux-xfs@vger.kernel.org>,
        Ross Zwisler <zwisler@kernel.org>,
        Vishal L Verma <vishal.l.verma@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Christoph Hellwig <hch@infradead.org>,
        Len Brown <lenb@kernel.org>, Jan Kara <jack@suse.cz>,
        "Theodore Ts'o" <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        lcapitulino@redhat.com, Kevin Wolf <kwolf@redhat.com>,
        Igor Mammedov <imammedo@redhat.com>,
        jmoyer <jmoyer@redhat.com>,
        Nitesh Narayan Lal <nilal@redhat.com>,
        Rik van Riel <riel@surriel.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        david <david@fromorbit.com>, cohuck@redhat.com,
        Xiao Guangrong <xiaoguangrong.eric@gmail.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Adam Borowski <kilobyte@angband.pl>,
        yuval shaia <yuval.shaia@oracle.com>, jstaron@google.com
Content-Type: text/plain; charset="UTF-8"
Sender: linux-ext4-owner@vger.kernel.org
Precedence: bulk

On Fri, May 10, 2019 at 8:53 AM Pankaj Gupta <pagupta@redhat.com> wrote:
>
> This patch adds 'DAXDEV_SYNC' flag which is set
> for nd_region doing synchronous flush. This later
> is used to disable MAP_SYNC functionality for
> ext4 & xfs filesystem for devices don't support
> synchronous flush.
>
> Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> ---
>  drivers/dax/bus.c            |  2 +-
>  drivers/dax/super.c          | 13 ++++++++++++-
>  drivers/md/dm.c              |  3 ++-
>  drivers/nvdimm/pmem.c        |  5 ++++-
>  drivers/nvdimm/region_devs.c |  7 +++++++
>  include/linux/dax.h          |  8 ++++++--
>  include/linux/libnvdimm.h    |  1 +
>  7 files changed, 33 insertions(+), 6 deletions(-)
[..]
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 043f0761e4a0..ee007b75d9fd 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1969,7 +1969,8 @@ static struct mapped_device *alloc_dev(int minor)
>         sprintf(md->disk->disk_name, "dm-%d", minor);
>
>         if (IS_ENABLED(CONFIG_DAX_DRIVER)) {
> -               dax_dev = alloc_dax(md, md->disk->disk_name, &dm_dax_ops);
> +               dax_dev = alloc_dax(md, md->disk->disk_name, &dm_dax_ops,
> +                                                        DAXDEV_F_SYNC);

Apologies for not realizing this until now, but this is broken.
Imaging a device-mapper configuration composed of both 'async'
virtio-pmem and 'sync' pmem. The 'sync' flag needs to be unified
across all members. I would change this argument to '0' and then
arrange for it to be set at dm_table_supports_dax() time after
validating that all components support synchronous dax.