diff --git a/Performance.md b/Performance.md
index fe961d9..ea50cf2 100644
--- a/Performance.md
+++ b/Performance.md
@@ -1,5 +1,7 @@
 Some basic notes on performance:
 
+DISCLAIMER: the memory footprint measurements documented on this page and graphed (see the hyperlinks below) are based on VmSize in linux. VmSize almost certainly doesn't correlated with what you care about. For example, it doesn't correlated very well at all with whether your server will go into swap thrash, or how much RAM you need to provision for your server, or, well, anything that you care about. Yes, in case it isn't clear, I (Zooko) consider this measurement to be useless. Please see ticket #227 in which I go into more detail about this.
+ 
 ## Memory Footprint
 
 We try to keep the Tahoe memory footprint low by continuously monitoring the