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-.\" Copyright (C) 1994, 1995, Daniel Quinlan <quinlan@yggdrasil.com>
-.\" Copyright (C) 2002-2008, 2017, Michael Kerrisk <mtk.manpages@gmail.com>
-.\" Copyright (C) 2023, Alejandro Colomar <alx@kernel.org>
-.\"
-.\" SPDX-License-Identifier: GPL-3.0-or-later
-.\"
-.TH proc_pid_io 5 2024-03-18 "Linux man-pages 6.7"
-.SH NAME
-/proc/pid/io \- I/O statistics
-.SH DESCRIPTION
-.TP
-.IR /proc/ pid /io " (since Linux 2.6.20)"
-.\" commit 7c3ab7381e79dfc7db14a67c6f4f3285664e1ec2
-This file contains I/O statistics
-for the process and its waited-for children,
-for example:
-.IP
-.in +4n
-.EX
-.RB "#" " cat /proc/3828/io"
-rchar: 323934931
-wchar: 323929600
-syscr: 632687
-syscw: 632675
-read_bytes: 0
-write_bytes: 323932160
-cancelled_write_bytes: 0
-.EE
-.in
-.IP
-The fields are as follows:
-.RS
-.TP
-.IR rchar ": characters read"
-The number of bytes
-returned by successful
-.BR read (2)
-and similar system calls.
-.TP
-.IR wchar ": characters written"
-The number of bytes
-returned by successful
-.BR write (2)
-and similar system calls.
-.TP
-.IR syscr ": read syscalls"
-The number of "file read" system calls\[em]those from the
-.BR read (2)
-family,
-.BR sendfile (2),
-.BR copy_file_range (2),
-and
-.BR ioctl (2)
-.BR BTRFS_IOC_ENCODED_READ [ _32 ]
-(including when invoked by the kernel as part of other syscalls).
-.TP
-.IR syscw ": write syscalls"
-The number of "file write" system calls\[em]those from the
-.BR write (2)
-family,
-.BR sendfile (2),
-.BR copy_file_range (2),
-and
-.BR ioctl (2)
-.BR BTRFS_IOC_ENCODED_WRITE [ _32 ]
-(including when invoked by the kernel as part of other syscalls).
-.TP
-.IR read_bytes ": bytes read"
-The number of bytes really fetched from the storage layer.
-This is accurate for block-backed filesystems.
-.TP
-.IR write_bytes ": bytes written"
-The number of bytes really sent to the storage layer.
-.TP
-.IR cancelled_write_bytes :
-The above statistics fail to account for truncation:
-if a process writes 1 MB to a regular file and then removes it,
-said 1 MB will not be written, but
-.I will
-have nevertheless been accounted as a 1 MB write.
-This field represents the number of bytes "saved" from I/O writeback.
-This can yield to having done negative I/O
-if caches dirtied by another process are truncated.
-.I cancelled_write_bytes
-applies to I/O already accounted-for in
-.IR write_bytes .
-.RE
-.IP
-Permission to access this file is governed by
-.BR ptrace (2)
-access mode
-.BR PTRACE_MODE_READ_FSCREDS .
-.SH CAVEATS
-These counters are not atomic:
-on systems where 64-bit integer operations may tear,
-a counter could be updated simultaneously with a read,
-yielding an incorrect intermediate value.
-.SH SEE ALSO
-.BR getrusage (2),
-.BR proc (5)