hugetlb: fix i_blocks accounting

For administrative purpose, we want to query actual block usage for
hugetlbfs file via fstat.  Currently, hugetlbfs always return 0.  Fix that
up since kernel already has all the information to track it properly.

Signed-off-by: Ken Chen <kenchen@google.com>
Acked-by: Adam Litke <agl@us.ibm.com>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/hugetlb.h

@@ -168,6 +168,8 @@ struct file *hugetlb_file_setup(const char *name, size_t);
 int hugetlb_get_quota(struct address_space *mapping, long delta);
 void hugetlb_put_quota(struct address_space *mapping, long delta);
 
+#define BLOCKS_PER_HUGEPAGE	(HPAGE_SIZE / 512)
+
 static inline int is_file_hugepages(struct file *file)
 {
 	if (file->f_op == &hugetlbfs_file_operations)

mm/hugetlb.c

@@ -801,6 +801,7 @@ retry:
 
 		if (vma->vm_flags & VM_SHARED) {
 			int err;
+			struct inode *inode = mapping->host;
 
 			err = add_to_page_cache(page, mapping, idx, GFP_KERNEL);
 			if (err) {
@@ -809,6 +810,10 @@ retry:
 					goto retry;
 				goto out;
 			}
+
+			spin_lock(&inode->i_lock);
+			inode->i_blocks += BLOCKS_PER_HUGEPAGE;
+			spin_unlock(&inode->i_lock);
 		} else
 			lock_page(page);
 	}
@@ -1160,6 +1165,11 @@ int hugetlb_reserve_pages(struct inode *inode, long from, long to)
 void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed)
 {
 	long chg = region_truncate(&inode->i_mapping->private_list, offset);
+
+	spin_lock(&inode->i_lock);
+	inode->i_blocks -= BLOCKS_PER_HUGEPAGE * freed;
+	spin_unlock(&inode->i_lock);
+
 	hugetlb_put_quota(inode->i_mapping, (chg - freed));
 	hugetlb_acct_memory(-(chg - freed));
 }