Linux Virtualization - May 2019 - [PATCH v8 3/6] libnvdimm: add dax_dev sync flag

On Fri, May 10, 2019 at 8:53 AM Pankaj Gupta <pagupta at 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 at 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.

> >
> > 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 at 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.
o.k. Need to set 'DAXDEV_F_SYNC' flag after verifying all the target
components support synchronous DAX.

Just a question, If device mapper configuration have composed of both 
virtio-pmem or pmem devices, we want to configure device mapper for async flush?

Thank you,
Pankaj 
>

On Fri, May 10, 2019 at 5:45 PM Pankaj Gupta <pagupta at 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 at 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.
>
> o.k. Need to set 'DAXDEV_F_SYNC' flag after verifying all the
target
> components support synchronous DAX.
>
> Just a question, If device mapper configuration have composed of both
> virtio-pmem or pmem devices, we want to configure device mapper for async
flush?
If it's composed of both then, yes, it needs to be async flush at the
device-mapper level. Otherwise MAP_SYNC will succeed and fail to
trigger fsync on the host file when necessary for the virtio-pmem
backed portion of the device-mapper device.