Index: share/man/man9/vnode_pager_setsize.9
===================================================================
--- share/man/man9/vnode_pager_setsize.9
+++ share/man/man9/vnode_pager_setsize.9
@@ -27,7 +27,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd April 6, 2021
+.Dd April 8, 2021
 .Dt VNODE_PAGER_SETSIZE 9
 .Os
 .Sh NAME
@@ -42,13 +42,23 @@
 .Sh DESCRIPTION
 .Nm
 lets the VM system know about a change in size for a file.
-Content beyond the new EOF specified by the
-.Fa nsize
-argument will be purged from the cache.
+Content between the old EOF and the new EOF will be purged from the cache
+if the file size shrinks.
+In case the vnode
+.Fa vp
+does not have a VM object, the effect of calling this function is no-op.
+.Pp
+The new EOF is rounded up to the nearest page index as a boundary
+within which the page fault handler should handle.
+.Pp
 This function is useful for use within file system code to implement
 truncation in
 .Xr VOP_SETATTR 9 .
 .Sh IMPLEMENTATION NOTES
+The function updates the object size of the vm object in
+.Fa vp
+with the new EOF specified by the
+.Fa nsize .
 In case the new EOF specified by the
 .Fa nsize
 argument is not aligned to page boundaries,
@@ -57,10 +67,8 @@
 for content occupying whole blocks within block
 boundaries,
 the dirty bits for the corresponding blocks will be cleared.
-.Sh LOCKING
-Writer lock of the VM object of
-.Fa vp
-will be held within the function.
+.Sh LOCKS
+The vnode should be exclusively locked on entry and will still be locked on exit.
 .Sh SEE ALSO
 .Xr vnode 9
 .Sh HISTORY