Bug#257827: munin-node: memory graph reports negative values.

[Juha-Matti Tapio]

I think I have found a solution for this bug.

>From what I have observed and read, VmallocUsed and SwapCached should not be
included in the stack forming total memory and they should not be deducted
from apps. Most of the servers I monitor do not have significant amount of
either of these, but on three servers with memory hungry applications the
problem shows up (kernel versions 2.6.7, 2.6.12 and 2.6.15.1).

See my comment on Fri Apr 7 00:38:46 2006 here:
http://munin.projects.linpro.no/ticket/119

I think the attached patch should fix this bug.

--- munin-1.2.4/node/node.d.linux/memory.in     2005-10-08 13:10:59.000000000 
+0300
+++ memory      2006-04-07 01:27:00.000000000 +0300
@@ -68,14 +68,6 @@
                {
                        print "page_tables ";
                }
-               if (exists $mems{'SwapCached'})
-               {
-                       print "swap_cache ";
-               }
-               if (exists $mems{'VmallocUsed'})
-               {
-                       print "vmalloc_used ";
-               }
                if (exists $mems{'Slab'})
                {
                        print "slab ";
@@ -106,12 +98,6 @@
                print "slab.draw STACK\n";
                print "slab.info Memory used by the kernel (major users are 
caches like inode, dentry, etc).\n";
        }
-       if (exists $mems{'SwapCached'})
-       {
-               print "swap_cache.label swap_cache\n";
-               print "swap_cache.draw STACK\n";
-               print "swap_cache.info A piece of memory that keeps track of 
pages that have been fetched from swap but not yet been modified.\n";
-       }
        if (exists $mems{'PageTables'})
        {
                print "page_tables.label page_tables\n";
@@ -121,9 +107,15 @@
        if (exists $mems{'VmallocUsed'})
        {
                print "vmalloc_used.label vmalloc_used\n";
-               print "vmalloc_used.draw STACK\n";
+               print "vmalloc_used.draw LINE2\n";
                print "vmalloc_used.info Virtual memory used by the kernel 
(used when the memory does not have to be physically contigious).\n";
        }
+       if (exists $mems{'SwapCached'})
+       {
+               print "swap_cache.label swap_cache\n";
+               print "swap_cache.draw LINE2\n";
+               print "swap_cache.info A piece of memory that keeps track of 
pages that have been fetched from swap but not yet been modified.\n";
+       }
        if (exists $mems{'Committed_AS'})
        {
                print "committed.label committed\n";
@@ -190,14 +182,6 @@
 {
        $mems{'Slab'} = 0;
 }
-if (exists $mems{'SwapCached'})
-{
-       print "swap_cache.value ", $mems{'SwapCached'}, "\n";
-}
-else
-{
-       $mems{'SwapCached'} = 0;
-}
 if (exists $mems{'PageTables'})
 {
        print "page_tables.value ", $mems{'PageTables'}, "\n";
@@ -206,29 +190,35 @@
 {
        $mems{'PageTables'} = 0;
 }
-if (exists $mems{'VmallocUsed'})
-{
-       print "vmalloc_used.value ", $mems{'VmallocUsed'}, "\n";
-}
-else
-{
-       $mems{'VmallocUsed'} = 0;
-}
 
 print "apps.value ", $mems{'MemTotal'}
        -$mems{'MemFree'}
        -$mems{'Buffers'}
        -$mems{'Cached'}
-       -$mems{'SwapCached'}
        -$mems{'Slab'}
        -$mems{'PageTables'}
-       -$mems{'VmallocUsed'}
        ,"\n";
 print "free.value ", $mems{'MemFree'}, "\n";
 print "buffers.value ", $mems{'Buffers'}, "\n";
 print "cached.value ", $mems{'Cached'}, "\n";
 print "swap.value ", $mems{'SwapTotal'} - $mems{'SwapFree'}, "\n";
 
+if (exists $mems{'SwapCached'})
+{
+       print "swap_cache.value ", $mems{'SwapCached'}, "\n";
+}
+else
+{
+       $mems{'SwapCached'} = 0;
+}
+if (exists $mems{'VmallocUsed'})
+{
+       print "vmalloc_used.value ", $mems{'VmallocUsed'}, "\n";
+}
+else
+{
+       $mems{'VmallocUsed'} = 0;
+}
 if (exists $mems{'Committed_AS'})
 {
        print "committed.value ", $mems{'Committed_AS'}, "\n";