diff -up man-pages-3.53/man5/proc.5.orig man-pages-3.53/man5/proc.5
--- man-pages-3.53/man5/proc.5.orig	2013-07-31 08:45:56.000000000 +0200
+++ man-pages-3.53/man5/proc.5	2013-08-02 13:00:55.062278000 +0200
@@ -59,7 +59,7 @@
 .\" to see what information could be imported from that file
 .\" into this file.
 .\"
-.TH PROC 5 2013-06-27 "Linux" "Linux Programmer's Manual"
+.TH PROC 5 2013-08-01 "Linux" "Linux Programmer's Manual"
 .SH NAME
 proc \- process information pseudo-file system
 .SH DESCRIPTION
@@ -350,9 +350,88 @@ file access mode and file status flags (
 .BR open (2)).
 
 The files in this directory are readable only by the owner of the process.
-.\" FIXME document /proc/[pid]/io
-.\" .TP
-.\" .IR /proc/[pid]/io " (since kernel 2.6.20)"
+.TP
+.IR /proc/[pid]/io " (since kernel 2.6.20)"
+.\" commit 7c3ab7381e79dfc7db14a67c6f4f3285664e1ec2
+This file contains I/O statistics for the process, for example:
+.in +4n
+.nf
+
+.RB "#" " cat /proc/3828/io"
+rchar: 323934931
+wchar: 323929600
+syscr: 632687
+syscw: 632675
+read_bytes: 0
+write_bytes: 323932160
+cancelled_write_bytes: 0
+.fi
+.in
+
+The fields are as follows:
+.RS
+.TP
+.IR rchar ": characters read"
+The number of bytes which this task has caused to be read from storage.
+This is simply the sum of bytes which this process passed to
+.BR read (2)
+and similar system calls.
+It includes things such as terminal I/O and 
+is unaffected by whether or not actual
+physical disk I/O was required (the read might have been satisfied from
+pagecache).
+.TP
+.IR wchar ": characters written"
+The number of bytes which this task has caused, or shall cause to be written
+to disk.
+Similar caveats apply here as with
+.IR rchar .
+.TP
+.IR syscr ": read syscalls"
+Attempt to count the number of read I/O operations\(emthat is,
+system calls such as
+.BR read (2)
+and
+.BR pread (2).
+.TP
+.IR syscw ": write syscalls"
+Attempt to count the number of write I/O operations\(emthat is,
+system calls such as
+.BR write (2)
+and
+.BR pwrite (2).
+.TP
+.IR read_bytes ": bytes read"
+Attempt to count the number of bytes which this process really did cause to
+be fetched from the storage layer.
+This is accurate for block-backed filesystems.
+.TP
+.IR write_bytes ": bytes written"
+Attempt to count the number of bytes which this process caused to be sent to
+the storage layer.
+.TP
+.IR cancelled_write_bytes :
+The big inaccuracy here is truncate.
+If a process writes 1MB to a file and then deletes the file,
+it will in fact perform no writeout.
+But it will have been accounted as having caused 1MB of write.
+In other words: this field represents the number of bytes which this process
+caused to not happen, by truncating pagecache.
+A task can cause "negative" I/O too.
+If this task truncates some dirty pagecache,
+some I/O which another task has been accounted for
+(in its
+.IR write_bytes )
+will not be happening.
+.RE
+.IP
+.IR Note :
+In the current implementation, things are a bit racy on 32-bit systems:
+if process A reads process B's
+.I /proc/[pid]/io
+while process B is updating one of these 64-bit counters,
+process A could see an intermediate result.
+.RE
 .TP
 .IR /proc/[pid]/limits " (since kernel 2.6.24)"
 This file displays the soft limit, hard limit, and units of measurement