Messages in this thread | | | From | "Verma, Vishal L" <> | Subject | Re: [PATCH v3 2/2] dax: add a sysfs knob to control memmap_on_memory behavior | Date | Tue, 12 Dec 2023 00:40:57 +0000 |
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On Tue, 2023-12-12 at 08:30 +0800, Huang, Ying wrote: > Vishal Verma <vishal.l.verma@intel.com> writes: > > > Add a sysfs knob for dax devices to control the memmap_on_memory setting > > if the dax device were to be hotplugged as system memory. > > > > The default memmap_on_memory setting for dax devices originating via > > pmem or hmem is set to 'false' - i.e. no memmap_on_memory semantics, to > > preserve legacy behavior. For dax devices via CXL, the default is on. > > The sysfs control allows the administrator to override the above > > defaults if needed. > > > > Cc: David Hildenbrand <david@redhat.com> > > Cc: Dan Williams <dan.j.williams@intel.com> > > Cc: Dave Jiang <dave.jiang@intel.com> > > Cc: Dave Hansen <dave.hansen@linux.intel.com> > > Cc: Huang Ying <ying.huang@intel.com> > > Tested-by: Li Zhijian <lizhijian@fujitsu.com> > > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> > > Reviewed-by: David Hildenbrand <david@redhat.com> > > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com> > > --- > > drivers/dax/bus.c | 47 +++++++++++++++++++++++++++++++++ > > Documentation/ABI/testing/sysfs-bus-dax | 17 ++++++++++++ > > 2 files changed, 64 insertions(+) > > > > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c > > index 1ff1ab5fa105..2871e5188f0d 100644 > > --- a/drivers/dax/bus.c > > +++ b/drivers/dax/bus.c > > @@ -1270,6 +1270,52 @@ static ssize_t numa_node_show(struct device *dev, > > } > > static DEVICE_ATTR_RO(numa_node); > > > > +static ssize_t memmap_on_memory_show(struct device *dev, > > + struct device_attribute *attr, char *buf) > > +{ > > + struct dev_dax *dev_dax = to_dev_dax(dev); > > + > > + return sprintf(buf, "%d\n", dev_dax->memmap_on_memory); > > +} > > + > > +static ssize_t memmap_on_memory_store(struct device *dev, > > + struct device_attribute *attr, > > + const char *buf, size_t len) > > +{ > > + struct device_driver *drv = dev->driver; > > + struct dev_dax *dev_dax = to_dev_dax(dev); > > + struct dax_region *dax_region = dev_dax->region; > > + struct dax_device_driver *dax_drv = to_dax_drv(drv); > > + ssize_t rc; > > + bool val; > > + > > + rc = kstrtobool(buf, &val); > > + if (rc) > > + return rc; > > + > > + if (dev_dax->memmap_on_memory == val) > > + return len; > > + > > + device_lock(dax_region->dev); > > + if (!dax_region->dev->driver) { > > + device_unlock(dax_region->dev); > > + return -ENXIO; > > + } > > I think that it should be OK to write to "memmap_on_memory" if no driver > is bound to the device. We just need to avoid to write to it when kmem > driver is bound.
Oh this is just a check on the region driver, not for a dax driver being bound to the device. It's the same as what things like align_store(), size_store() etc. do for dax device reconfiguration.
That said, it might be okay to remove this check, as this operation doesn't change any attributes of the dax region (the other interfaces I mentioned above can affect regions, so we want to lock the region device). If removing the check, we'd drop the region lock acquisition as well.
Dan, any thoughts on this?
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