diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
index 4cc7cfdb8..73bd883af 100644
--- a/man2/ioctl_userfaultfd.2
+++ b/man2/ioctl_userfaultfd.2
@@ -85,9 +85,9 @@ structure, defined as:
 .nf
 
 struct uffdio_api {
-    __u64 api;
-    __u64 features;
-    __u64 ioctls;
+    __u64 api;        /* Requested API version (input) */
+    __u64 features;   /* Must be zero */
+    __u64 ioctls;     /* Available ioctl() operations (output) */
 };
 
 .fi
@@ -171,14 +171,14 @@ structure, defined as:
 .nf
 
 struct uffdio_range {
-    __u64 start;
-    __u64 len;
+    __u64 start;    /* Start of range */
+    __u64 len;      /* Length of rnage (bytes) */
 };
 
 struct uffdio_register {
     struct uffdio_range range;
-    __u64 mode;
-    __u64 ioctls;
+    __u64 mode;     /* Desired mode of operation (input) */
+    __u64 ioctls;   /* Available ioctl() operations (output) */
 };
 
 .fi
@@ -300,11 +300,11 @@ structure pointed to by
 .in +4n
 .nf
 struct uffdio_copy {
-    __u64 dst;
-    __u64 src;
-    __u64 len;
-    __u64 mode;
-    __s64 copy;
+    __u64 dst;    /* Source of copy */
+    __u64 src;    /* Destinate of copy */
+    __u64 len;    /* Number of bytes to copy */
+    __u64 mode;   /* Flags controlling behavior of copy */
+    __s64 copy;   /* Number of bytes copied, or negated error */
 };
 .fi
 .in
@@ -389,8 +389,8 @@ structure pointed to by
 .nf
 struct uffdio_zeropage {
     struct uffdio_range range;
-    __u64 mode;
-    __s64 zeropage;
+    __u64 mode;     /* Flags controlling behavior of copy */
+    __s64 zeropage; /* Number of bytes zeroed, or negated error */
 };
 .fi
 .in