/ proc / [pid] / ioのカウンターはどういう意味ですか？

Question

名前付きプロセスの統計を監視するための Munin のプラグインを作成しています。情報源の1つは /proc/[pid]/io です。しかし、rchar/wcharとread_bytes/written_bytesの違いを見つけるのは難しいです。

それらは異なる値を提供するため、同じではありません。彼らは何を表していますか？

Answer 1

proc manpage はひどく遅れています（したがって、ほとんどのマンページ/ドキュメントはcookie-cutterのユーザースペース開発に関連しないものにあります）が、幸運にも Linuxカーネルに完全にドキュメント化されていますソースDocumentation/filesystems/proc.txt 。関連するビットは次のとおりです。

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.