proc.5: Improve /proc/[pid]/smaps entries description

Glued together from:

https://www.kernel.org/doc/Documentation/filesystems/proc.txt
https://lkml.org/lkml/2008/9/23/362
https://lkml.org/lkml/2010/8/18/46

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man5/proc.5

@@ -975,13 +975,21 @@ For each of mappings there is a series of lines such as the following:
 .in +4n
 .nf
 
-08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
-Size:               464 kB
-Rss:                424 kB
-Shared_Clean:       424 kB
-Shared_Dirty:         0 kB
-Private_Clean:        0 kB
-Private_Dirty:        0 kB
+00400000-0048a000 r-xp 00000000 fd:03 960637                             /bin/bash
+Size:                552 kB
+Rss:                 460 kB
+Pss:                 100 kB
+Shared_Clean:        452 kB
+Shared_Dirty:          0 kB
+Private_Clean:         8 kB
+Private_Dirty:         0 kB
+Referenced:          460 kB
+Anonymous:             0 kB
+AnonHugePages:         0 kB
+Swap:                  0 kB
+KernelPageSize:        4 kB
+MMUPageSize:           4 kB
+Locked:                0 kB
 
 .fi
 .in
@@ -989,9 +997,56 @@ The first of these lines shows the same information as is displayed
 for the mapping in
 .IR /proc/[pid]/maps .
 The remaining lines show the size of the mapping,
-the amount of the mapping that is currently resident in RAM,
-the number of clean and dirty shared pages in the mapping,
+the amount of the mapping that is currently resident in RAM ("Rss"),
+the process' proportional share of this mapping ("Pss"),
+the number of clean and dirty shared pages in the mapping
 and the number of clean and dirty private pages in the mapping.
+"Referenced" indicates the amount of memory currently marked as
+referenced or accessed. "Anonymous" shows the amount of memory
+that does not belong to any file.  "Swap" shows how much
+would-be-anonymous memory is also used, but out on swap.
+
+The "KernelPageSize" entry  is the pagesize used by the kernel to
+back a VMA. This matches the size used by the MMU in the majority
+of cases. However, one counter-example occurs on PPC64 kernels
+whereby a kernel using 64K as a base pagesize may still use 4K
+pages for the MMU on older processor. To distinguish, this
+patch reports "MMUPageSize" as the pagesize used by the MMU.
+
+The "Locked" indicates whether the mapping is locked in memory
+or not.
+
+"VmFlags" field represents the kernel flags associated with
+the particular virtual memory area in two letter encoded
+manner. The codes are the following:
+    rd  - readable
+    wr  - writeable
+    ex  - executable
+    sh  - shared
+    mr  - may read
+    mw  - may write
+    me  - may execute
+    ms  - may share
+    gd  - stack segment growns down
+    pf  - pure PFN range
+    dw  - disabled write to the mapped file
+    lo  - pages are locked in memory
+    io  - memory mapped I/O area
+    sr  - sequential read advise provided
+    rr  - random read advise provided
+    dc  - do not copy area on fork
+    de  - do not expand area on remapping
+    ac  - area is accountable
+    nr  - swap space is not reserved for the area
+    ht  - area uses huge tlb pages
+    nl  - non-linear mapping
+    ar  - architecture specific flag
+    dd  - do not include area into core dump
+    sd  - soft-dirty flag
+    mm  - mixed map area
+    hg  - huge page advise flag
+    nh  - no-huge page advise flag
+    mg  - mergable advise flag
 
 This file is present only if the
 .B CONFIG_MMU