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Date:   Fri, 10 May 2019 20:45:49 -0400 (EDT)
From:   Pankaj Gupta <pagupta@redhat.com>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     linux-nvdimm <linux-nvdimm@lists.01.org>,
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References: <20190510155202.14737-1-pagupta@redhat.com> <20190510155202.14737-4-pagupta@redhat.com> <CAPcyv4hbVNRFSyS2CTbmO88uhnbeH4eiukAng2cxgbDzLfizwg@mail.gmail.com>
Subject: Re: [PATCH v8 3/6] libnvdimm: add dax_dev sync flag
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Thread-Topic: libnvdimm: add dax_dev sync flag
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> >
> > 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 
>