dax: Use new dax zero page method for zeroing a page

Use new dax native zero page method for zeroing page if I/O is page
aligned. Otherwise fall back to direct_access() + memcpy().

This gets rid of one of the depenendency on block device in dax path.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Link: https://lore.kernel.org/r/20200228163456.1587-6-vgoyal@redhat.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

fs/dax.c

@@ -1038,47 +1038,40 @@ static vm_fault_t dax_load_hole(struct xa_state *xas,
 	return ret;
 }
 
-static bool dax_range_is_aligned(struct block_device *bdev,
-				 unsigned int offset, unsigned int length)
-{
-	unsigned short sector_size = bdev_logical_block_size(bdev);
-
-	if (!IS_ALIGNED(offset, sector_size))
-		return false;
-	if (!IS_ALIGNED(length, sector_size))
-		return false;
-
-	return true;
-}
-
 int __dax_zero_page_range(struct block_device *bdev,
 		struct dax_device *dax_dev, sector_t sector,
 		unsigned int offset, unsigned int size)
 {
-	if (dax_range_is_aligned(bdev, offset, size)) {
-		sector_t start_sector = sector + (offset >> 9);
-
-		return blkdev_issue_zeroout(bdev, start_sector,
-				size >> 9, GFP_NOFS, 0);
-	} else {
 	pgoff_t pgoff;
 	long rc, id;
 	void *kaddr;
+	bool page_aligned = false;
+
+
+	if (IS_ALIGNED(sector << SECTOR_SHIFT, PAGE_SIZE) &&
+	    IS_ALIGNED(size, PAGE_SIZE))
+		page_aligned = true;
 
 	rc = bdev_dax_pgoff(bdev, sector, PAGE_SIZE, &pgoff);
 	if (rc)
 		return rc;
 
 	id = dax_read_lock();
+
+	if (page_aligned)
+		rc = dax_zero_page_range(dax_dev, pgoff, size >> PAGE_SHIFT);
+	else
 		rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr, NULL);
 	if (rc < 0) {
 		dax_read_unlock(id);
 		return rc;
 	}
+
+	if (!page_aligned) {
 		memset(kaddr + offset, 0, size);
 		dax_flush(dax_dev, kaddr + offset, size);
-		dax_read_unlock(id);
 	}
+	dax_read_unlock(id);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(__dax_zero_page_range);