diff --git a/lib/libc/sys/copy_file_range.2.sav b/lib/libc/sys/copy_file_range.2
--- a/lib/libc/sys/copy_file_range.2.sav
+++ b/lib/libc/sys/copy_file_range.2
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD: head/lib/libc/sys/copy_file_range.2 359465 2020-03-30 21:44:00Z jhb $
 .\"
-.Dd March 30, 2020
+.Dd January 2, 2021
 .Dt COPY_FILE_RANGE 2
 .Os
 .Sh NAME
@@ -133,6 +133,15 @@
 .Fn copy_file_range
 should be used in a loop until copying of the desired byte range has been
 completed.
+For performance reasons, the
+.Fa len
+argument should be set to the largest value possible.
+For copying to EOF on the input file, the value may be SSIZE_MAX.
+Doing so reduces the number of system calls, along with
+associated SEEK_HOLE, SEEK_DATA operations done either by
+.Xr lseek 2
+or internally by
+.Fn copy_file_range .
 If an error has occurred, a \-1 is returned and the error code is placed in
 the global variable
 .Va errno .