[src/trunk]: src/sys/arch/alpha/include Additional comment about the range (0...

[thorpej <thorpej%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/6e0286fa2ef8
branches:  trunk
changeset: 1021470:6e0286fa2ef8
user:      thorpej <thorpej%NetBSD.org@localhost>
date:      Mon May 31 17:22:44 2021 +0000

description:
Additional comment about the range (0-1025) that's needed for the PT page
reference count, and thus now many bits we need to scare up.

diffstat:

 sys/arch/alpha/include/pmap.h |  6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diffs (20 lines):

diff -r 50d5372274d7 -r 6e0286fa2ef8 sys/arch/alpha/include/pmap.h
--- a/sys/arch/alpha/include/pmap.h     Mon May 31 17:16:04 2021 +0000
+++ b/sys/arch/alpha/include/pmap.h     Mon May 31 17:22:44 2021 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: pmap.h,v 1.97 2021/05/31 17:16:05 thorpej Exp $ */
+/* $NetBSD: pmap.h,v 1.98 2021/05/31 17:22:44 thorpej Exp $ */
 
 /*-
  * Copyright (c) 1998, 1999, 2000, 2001, 2007 The NetBSD Foundation, Inc.
@@ -360,6 +360,10 @@
         * XXX These fields are only needed for pages that are used
         * as PT pages.  It would be nice to find safely-unused fields
         * in the vm_page structure that could be used instead.
+        *
+        * (Only 11 bits are needed ... we need to be able to count from
+        * 0-1025 ... 1025 because sometimes we need to take an extra
+        * reference temporarily in pmap_enter().)
         */
        unsigned int pvh_physpgrefs;    /* # refs as a PT page */
        unsigned int pvh_spare0;        /* XXX spare field */