libnvdimm: Stop using HPAGE_SIZE

Currently libnvdimm uses HPAGE_SIZE as the default alignment for DAX and
PFN devices. HPAGE_SIZE is the default hugetlbfs page size and when
hugetlbfs is disabled it defaults to PAGE_SIZE. Given DAX has more
in common with THP than hugetlbfs we should proably be using
HPAGE_PMD_SIZE, but this is undefined when THP is disabled so lets just
give it a new name.

The other usage of HPAGE_SIZE in libnvdimm is when determining how large
the altmap should be. For the reasons mentioned above it doesn't really
make sense to use HPAGE_SIZE here either. PMD_SIZE seems to be safe to
use in generic code and it happens to match the vmemmap allocation block
on x86 and Power. It's still a hack, but it's a slightly nicer hack.
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/nd.h

@@ -285,6 +285,13 @@ static inline struct device *nd_btt_create(struct nd_region *nd_region)
 
 struct nd_pfn *to_nd_pfn(struct device *dev);
 #if IS_ENABLED(CONFIG_NVDIMM_PFN)
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#define PFN_DEFAULT_ALIGNMENT HPAGE_PMD_SIZE
+#else
+#define PFN_DEFAULT_ALIGNMENT PAGE_SIZE
+#endif
+
 int nd_pfn_probe(struct device *dev, struct nd_namespace_common *ndns);
 bool is_nd_pfn(struct device *dev);
 struct device *nd_pfn_create(struct nd_region *nd_region);

drivers/nvdimm/pfn_devs.c

@@ -290,7 +290,7 @@ struct device *nd_pfn_devinit(struct nd_pfn *nd_pfn,
 		return NULL;
 
 	nd_pfn->mode = PFN_MODE_NONE;
-	nd_pfn->align = HPAGE_SIZE;
+	nd_pfn->align = PFN_DEFAULT_ALIGNMENT;
 	dev = &nd_pfn->dev;
 	device_initialize(&nd_pfn->dev);
 	if (ndns && !__nd_attach_ndns(&nd_pfn->dev, ndns, &nd_pfn->ndns)) {
@@ -638,11 +638,12 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
 			/ PAGE_SIZE);
 	if (nd_pfn->mode == PFN_MODE_PMEM) {
 		/*
-		 * vmemmap_populate_hugepages() allocates the memmap array in
-		 * HPAGE_SIZE chunks.
+		 * The altmap should be padded out to the block size used
+		 * when populating the vmemmap. This *should* be equal to
+		 * PMD_SIZE for most architectures.
 		 */
 		offset = ALIGN(start + SZ_8K + 64 * npfns + dax_label_reserve,
-				max(nd_pfn->align, HPAGE_SIZE)) - start;
+				max(nd_pfn->align, PMD_SIZE)) - start;
 	} else if (nd_pfn->mode == PFN_MODE_RAM)
 		offset = ALIGN(start + SZ_8K + dax_label_reserve,
 				nd_pfn->align) - start;