[PATCH] /proc/meminfo documentation

From: Dave Hansen <haveblue@us.ibm.com>

Documents the information in /proc/meminfo

Documentation/filesystems/proc.txt

@@ -362,6 +362,93 @@ IDE devices:
   ide-cdrom version 4.53 
   ide-disk version 1.08 
 
+..............................................................................
+
+meminfo:
+
+Provides information about distribution and utilization of memory.  This
+varies by architecture and compile options.  The following is from a
+16GB PIII, which has highmem enabled.  You may not have all of these fields.
+
+> cat /proc/meminfo
+
+
+MemTotal:     16344972 kB
+MemFree:      13634064 kB
+Buffers:          3656 kB
+Cached:        1195708 kB
+SwapCached:          0 kB
+Active:         891636 kB
+Inactive:      1077224 kB
+HighTotal:    15597528 kB
+HighFree:     13629632 kB
+LowTotal:       747444 kB
+LowFree:          4432 kB
+SwapTotal:           0 kB
+SwapFree:            0 kB
+Dirty:             968 kB
+Writeback:           0 kB
+Mapped:         280372 kB
+Slab:           684068 kB
+Committed_AS:  1576424 kB
+PageTables:      24448 kB
+ReverseMaps:   1080904
+VmallocTotal:   112216 kB
+VmallocUsed:       428 kB
+VmallocChunk:   111088 kB
+
+    MemTotal: Total usable ram (i.e. physical ram minus a few reserved
+              bits and the kernel binary code)
+     MemFree: The sum of LowFree+HighFree
+     Buffers: Relatively temporary storage for raw disk blocks
+              shouldn't get tremendously large (20MB or so)
+      Cached: in-memory cache for files read from the disk (the
+              pagecache).  Doesn't include SwapCached
+  SwapCached: Memory that once was swapped out, is swapped back in but
+              still also is in the swapfile (if memory is needed it
+              doesn't need to be swapped out AGAIN because it is already
+              in the swapfile. This saves I/O)
+      Active: Memory that has been used more recently and usually not
+              reclaimed unless absolutely necessary.
+    Inactive: Memory which has been less recently used.  It is more
+              eligible to be reclaimed for other purposes
+   HighTotal:
+    HighFree: Highmem is all memory above ~860MB of physical memory
+              Highmem areas are for use by userspace programs, or
+              for the pagecache.  The kernel must use tricks to access
+              this memory, making it slower to access than lowmem.
+    LowTotal:
+     LowFree: Lowmem is memory which can be used for everything that
+              highmem can be used for, but it is also availble for the
+              kernel's use for its own data structures.  Among many
+              other things, it is where everything from the Slab is
+              allocated.  Bad things happen when you're out of lowmem.
+   SwapTotal: total amount of swap space available
+    SwapFree: Memory which has been evicted from RAM, and is temporarily
+              on the disk
+       Dirty: Memory which is waiting to get written back to the disk
+   Writeback: Memory which is actively being written back to the disk
+      Mapped: files which have been mmaped, such as libraries
+              Slab: in-kernel data structures cache
+Committed_AS: An estimate of how much RAM you would need to make a
+              99.99% guarantee that there never is OOM (out of memory)
+              for this workload. Normally the kernel will overcommit
+              memory. That means, say you do a 1GB malloc, nothing
+              happens, really. Only when you start USING that malloc
+              memory you will get real memory on demand, and just as
+              much as you use. So you sort of take a mortgage and hope
+              the bank doesn't go bust. Other cases might include when
+              you mmap a file that's shared only when you write to it
+              and you get a private copy of that data. While it normally
+              is shared between processes. The Committed_AS is a
+              guesstimate of how much RAM/swap you would need
+              worst-case.
+  PageTables: amount of memory dedicated to the lowest level of page
+              tables.
+ ReverseMaps: number of reverse mappings performed
+VmallocTotal: total size of vmalloc memory area
+ VmallocUsed: amount of vmalloc area which is used
+VmallocChunk: largest contigious block of vmalloc area which is free
 
 More detailed  information  can  be  found  in  the  controller  specific
 subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these