diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 79a797e..1fbd4eb 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -119,8 +119,11 @@
 
 dirty_background_ratio
 
-Contains, as a percentage of total system memory, the number of pages at which
-the background kernel flusher threads will start writing out dirty data.
+Contains, as a percentage of total available memory that contains free pages
+and reclaimable pages, the number of pages at which the background kernel
+flusher threads will start writing out dirty data.
+
+The total avaiable memory is not equal to total system memory.
 
 ==============================================================
 
@@ -151,9 +154,11 @@
 
 dirty_ratio
 
-Contains, as a percentage of total system memory, the number of pages at which
-a process which is generating disk writes will itself start writing out dirty
-data.
+Contains, as a percentage of total available memory that contains free pages
+and reclaimable pages, the number of pages at which a process which is
+generating disk writes will itself start writing out dirty data.
+
+The total avaiable memory is not equal to total system memory.
 
 ==============================================================