Re: [PATCH v8 3/6] libnvdimm: add dax_dev sync flag

Pankaj Gupta
2019-05-11T00:45:57Z

> >
> > 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.

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
>