libnvdimm, namespace: make min namespace size 4K

The arbitrary 4MB minimum namespace size turns out to be too large for
some environments. Quoting Cheng-mean Liu:

    In the case of emulated NVDIMM devices in the VM environment, there
    are scenarios that NVDIMM device with much smaller sizes are
    desired, for example, we might use a single enumerated NVDIMM DAX
    device for representing each container layer, which in some cases
    could be just a few KBs size.

PAGE_SIZE is the minimum where we can still support DAX of at least
a single page.

Cc: Matthew Wilcox <willy@infradead.org>
Reported-by: Cheng-mean Liu <soccerl@microsoft.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/include/uapi/linux/ndctl.h b/include/uapi/linux/ndctl.h
index 30ef1236aafa6e0345775f9edab56c5c929e06f0..7e27070b9440374f4c8e32187e8739c39318c889 100644 (file)
--- a/include/uapi/linux/ndctl.h
+++ b/include/uapi/linux/ndctl.h
@@ -209,7 +209,7 @@ enum nd_driver_flags {
 };
 
 enum {
-       ND_MIN_NAMESPACE_SIZE = 0x00400000,
+       ND_MIN_NAMESPACE_SIZE = PAGE_SIZE,
 };
 
 enum ars_masks {