/proc/[pid]/io 中的计数器是什么意思？

Question

我正在为Munin 创建一个插件来监控命名进程的统计信息。信息来源之一是/proc/[pid]/io。但我很难找出rchar/wchar 和read_bytes/written_bytes 之间的区别。

它们不一样，因为它们提供不同的值。它们代表什么？

Answer 1

虽然proc manpage 严重落后（大多数与千篇一律的用户空间开发无关的手册页/文档也是如此），幸运的是，这些内容完全记录在Linux kernel source 下的Documentation/filesystems/proc.rst 中。以下是相关位：

rchar
-----

I/O counter: chars 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 read() and pread().
It includes things like tty IO and it is unaffected by whether or not actual
physical disk IO was required (the read might have been satisfied from
pagecache)


wchar
-----

I/O counter: chars written
The number of bytes which this task has caused, or shall cause to be written
to disk. Similar caveats apply here as with rchar.


read_bytes
----------

I/O counter: bytes read
Attempt to count the number of bytes which this process really did cause to
be fetched from the storage layer. Done at the submit_bio() level, so it is
accurate for block-backed filesystems. <please add status regarding NFS and
CIFS at a later time>


write_bytes
-----------

I/O counter: bytes written
Attempt to count the number of bytes which this process caused to be sent to
the storage layer. This is done at page-dirtying time.