Re: [PATCH v3 3/5] libnvdimm: add nd_region buffered dax_dev flag
> >
> > This patch adds 'DAXDEV_BUFFERED' flag which is set
> > for virtio pmem corresponding nd_region. This later
> > is used to disable MAP_SYNC functionality for ext4
> > & xfs filesystem.
> >
> > Signed-off-by: Pankaj Gupta
> > ---
> > drivers/dax/super.c | 17 +
> > drivers/nvdimm/pmem.c| 3 +++
> > drivers/nvdimm/region_devs.c | 7 +++
> > drivers/virtio/pmem.c| 1 +
> > include/linux/dax.h | 9 +
> > include/linux/libnvdimm.h| 6 ++
> > 6 files changed, 43 insertions(+)
> >
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index 6e928f3..9128740 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -167,6 +167,8 @@ enum dax_device_flags {
> > DAXDEV_ALIVE,
> > /* gate whether dax_flush() calls the low level flush routine */
> > DAXDEV_WRITE_CACHE,
> > + /* flag to disable MAP_SYNC for virtio based host page cache flush
> > */
> > + DAXDEV_BUFFERED,
> > };
> >
> > /**
> > @@ -335,6 +337,21 @@ bool dax_write_cache_enabled(struct dax_device
> > *dax_dev)
> > }
> > EXPORT_SYMBOL_GPL(dax_write_cache_enabled);
> >
> > +void virtio_pmem_host_cache(struct dax_device *dax_dev, bool wc)
> > +{
> > + if (wc)
> > + set_bit(DAXDEV_BUFFERED, _dev->flags);
> > + else
> > + clear_bit(DAXDEV_BUFFERED, _dev->flags);
> > +}
> > +EXPORT_SYMBOL_GPL(virtio_pmem_host_cache);
>
> The "write_cache" property was structured this way because it can
> conceivably change at runtime. The MAP_SYNC capability should be
> static and never changed after init.
o.k. Will change.
>
> > +bool virtio_pmem_host_cache_enabled(struct dax_device *dax_dev)
> > +{
> > + return test_bit(DAXDEV_BUFFERED, _dev->flags);
> > +}
> > +EXPORT_SYMBOL_GPL(virtio_pmem_host_cache_enabled);
>
> Echoing Darrick and Jan this is should be a generic property of a
> dax_device and not specific to virtio. I don't like the "buffered"
> designation as that's not accurate. There may be hardware reasons why
> a dax_device is not synchronous, like a requirement to flush a
> write-pending queue or otherwise notify the device of new writes.
Agree.
>
> I would just have a dax_synchronous() helper and a DAXDEV_SYNC flag. I
> would also modify alloc_dax() to take a flags argument so that the
> capability can be instantiated when the dax_device is allocated.
o.k. Will make the change.
Thanks,
Pankaj
>
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Re: [PATCH v3 3/5] libnvdimm: add nd_region buffered dax_dev flag
On Wed, Jan 9, 2019 at 5:53 AM Pankaj Gupta wrote:
>
> This patch adds 'DAXDEV_BUFFERED' flag which is set
> for virtio pmem corresponding nd_region. This later
> is used to disable MAP_SYNC functionality for ext4
> & xfs filesystem.
>
> Signed-off-by: Pankaj Gupta
> ---
> drivers/dax/super.c | 17 +
> drivers/nvdimm/pmem.c| 3 +++
> drivers/nvdimm/region_devs.c | 7 +++
> drivers/virtio/pmem.c| 1 +
> include/linux/dax.h | 9 +
> include/linux/libnvdimm.h| 6 ++
> 6 files changed, 43 insertions(+)
>
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 6e928f3..9128740 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -167,6 +167,8 @@ enum dax_device_flags {
> DAXDEV_ALIVE,
> /* gate whether dax_flush() calls the low level flush routine */
> DAXDEV_WRITE_CACHE,
> + /* flag to disable MAP_SYNC for virtio based host page cache flush */
> + DAXDEV_BUFFERED,
> };
>
> /**
> @@ -335,6 +337,21 @@ bool dax_write_cache_enabled(struct dax_device *dax_dev)
> }
> EXPORT_SYMBOL_GPL(dax_write_cache_enabled);
>
> +void virtio_pmem_host_cache(struct dax_device *dax_dev, bool wc)
> +{
> + if (wc)
> + set_bit(DAXDEV_BUFFERED, _dev->flags);
> + else
> + clear_bit(DAXDEV_BUFFERED, _dev->flags);
> +}
> +EXPORT_SYMBOL_GPL(virtio_pmem_host_cache);
The "write_cache" property was structured this way because it can
conceivably change at runtime. The MAP_SYNC capability should be
static and never changed after init.
> +bool virtio_pmem_host_cache_enabled(struct dax_device *dax_dev)
> +{
> + return test_bit(DAXDEV_BUFFERED, _dev->flags);
> +}
> +EXPORT_SYMBOL_GPL(virtio_pmem_host_cache_enabled);
Echoing Darrick and Jan this is should be a generic property of a
dax_device and not specific to virtio. I don't like the "buffered"
designation as that's not accurate. There may be hardware reasons why
a dax_device is not synchronous, like a requirement to flush a
write-pending queue or otherwise notify the device of new writes.
I would just have a dax_synchronous() helper and a DAXDEV_SYNC flag. I
would also modify alloc_dax() to take a flags argument so that the
capability can be instantiated when the dax_device is allocated.
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