linux-kernel - Re: [PATCH 02/19] dax: Pass dax_dev to dax_writeback_mapping

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Date:   Fri, 3 Jan 2020 10:12:09 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>, virtio-fs@...hat.com,
        Miklos Szeredi <miklos@...redi.hu>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 02/19] dax: Pass dax_dev to dax_writeback_mapping_range()

On Fri, Jan 3, 2020 at 6:12 AM Vivek Goyal <vgoyal@...hat.com> wrote:
>
> On Mon, Aug 26, 2019 at 04:58:29PM -0400, Vivek Goyal wrote:
> > On Mon, Aug 26, 2019 at 04:33:26PM -0400, Vivek Goyal wrote:
> > > On Mon, Aug 26, 2019 at 04:53:16AM -0700, Christoph Hellwig wrote:
> > > > On Wed, Aug 21, 2019 at 01:57:03PM -0400, Vivek Goyal wrote:
> > > > > Right now dax_writeback_mapping_range() is passed a bdev and dax_dev
> > > > > is searched from that bdev name.
> > > > >
> > > > > virtio-fs does not have a bdev. So pass in dax_dev also to
> > > > > dax_writeback_mapping_range(). If dax_dev is passed in, bdev is not
> > > > > used otherwise dax_dev is searched using bdev.
> > > >
> > > > Please just pass in only the dax_device and get rid of the block device.
> > > > The callers should have one at hand easily, e.g. for XFS just call
> > > > xfs_find_daxdev_for_inode instead of xfs_find_bdev_for_inode.
> > >
> > > Sure. Here is the updated patch.
> > >
> > > This patch can probably go upstream independently. If you are fine with
> > > the patch, I can post it separately for inclusion.
> >
> > Forgot to update function declaration in case of !CONFIG_FS_DAX. Here is
> > the updated patch.
> >
> > Subject: dax: Pass dax_dev instead of bdev to dax_writeback_mapping_range()
> >
> > As of now dax_writeback_mapping_range() takes "struct block_device" as a
> > parameter and dax_dev is searched from bdev name. This also involves taking
> > a fresh reference on dax_dev and putting that reference at the end of
> > function.
> >
> > We are developing a new filesystem virtio-fs and using dax to access host
> > page cache directly. But there is no block device. IOW, we want to make
> > use of dax but want to get rid of this assumption that there is always
> > a block device associated with dax_dev.
> >
> > So pass in "struct dax_device" as parameter instead of bdev.
> >
> > ext2/ext4/xfs are current users and they already have a reference on
> > dax_device. So there is no need to take reference and drop reference to
> > dax_device on each call of this function.
> >
> > Suggested-by: Christoph Hellwig <hch@...radead.org>
> > Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
>
> Hi Dan,
>
> Ping for this patch. I see christoph and Jan acked it. Can we take it. Not
> sure how to get ack from ext4 developers.

Jan counts for ext4, I just missed this. Now merged.