[src/trunk]: src/usr.sbin/puffs/rump_tmpfs add ranty rant about data storage ...

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

details:   https://anonhg.NetBSD.org/src/rev/bc062e681ed6
branches:  trunk
changeset: 750115:bc062e681ed6
user:      pooka <pooka%NetBSD.org@localhost>
date:      Thu Dec 17 14:06:38 2009 +0000

description:
add ranty rant about data storage in tmpfs

diffstat:

 usr.sbin/puffs/rump_tmpfs/rump_tmpfs.c |  13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diffs (27 lines):

diff -r fb0c355495c0 -r bc062e681ed6 usr.sbin/puffs/rump_tmpfs/rump_tmpfs.c
--- a/usr.sbin/puffs/rump_tmpfs/rump_tmpfs.c    Thu Dec 17 12:49:22 2009 +0000
+++ b/usr.sbin/puffs/rump_tmpfs/rump_tmpfs.c    Thu Dec 17 14:06:38 2009 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: rump_tmpfs.c,v 1.3 2008/09/04 15:34:56 pooka Exp $     */
+/*     $NetBSD: rump_tmpfs.c,v 1.4 2009/12/17 14:06:38 pooka Exp $     */
 
 /*
  * Copyright (c) 2008 Antti Kantee.  All Rights Reserved.
@@ -39,6 +39,17 @@
 
 #include "mount_tmpfs.h"
 
+/*
+ * tmpfs has a slight "issue" with file content storage.  Since it
+ * stores data in memory, we will end up using 2x the RAM for
+ * storage if we cache in puffs vfs.  If we don't, we need to take
+ * the slow path from the kernel to the file server every time the
+ * file is accessed.  It's either suck or suck.  However, rump_tmpfs
+ * will not be used in real life, so this is hardly a release-stopping
+ * issue of catastrophic proportions.  For now we opt for un-double
+ * storage (PUFFS_KFLAG_NOCACHE_PAGE).
+ */
+
 int
 main(int argc, char *argv[])
 {