anchor.diff:    (pager-rpc 'protect-memory-range-in-pager base length flags))
   
   (defun protect-memory-range-in-pager (base length flags)
  -  (when *pager-noisy*
  -    (debug-print-line "Protect range " base "-" (+ base length) "  " flags))
  +  (pager-log "Protect range " base "-" (+ base length) "  " flags)
     (with-mutex (*vm-lock*)
       (dotimes (i (truncate length #x1000))
         ;; Update block map.
  
positive.code:       ;; Examine the page table, if there's a present entry then the page
        ;; was mapped while acquiring the VM lock. Just return.
        (when (page-present-p pte 0)
          (when (and (logtest (sys.int::memref-unsigned-byte-64 pte 0) +page-table-copy-on-write+)
                     *pager-noisy*)
            (debug-print-line "Copying page " address " in WFP.")
            (snapshot-clone-cow-page (pager-allocate-page) address))
          #+(or)(debug-print-line "WFP " address " block " block-info " already mapped " (page-table-entry pte 0))
          (return-from wait-for-page t))
  
negative.code:              (is-zero-page nil))
          (setf (physical-page-frame-block-id frame) (ldb (byte sys.int::+block-map-id-size+ sys.int::+block-map-id-shift+) block-info)
                (physical-page-virtual-address frame) (logand address (lognot (1- +4k-page-size+))))
          (when (not *page-replacement-list-head*)
            (pager-log "addr " address " vaddr " (physical-page-virtual-address frame) " frame " frame " pteA " (get-pte-for-address address #+(or)(physical-page-virtual-address frame) nil) " pteB " (get-pte-for-address (physical-page-virtual-address frame) nil)))
          (append-to-page-replacement-list frame)
          (cond ((logtest sys.int::+block-map-zero-fill+ block-info)
                 ;; Block is zero-filled.
  