This file is like getrusage(2) RUSAGE_SELF + RUSAGE_CHILDREN,
the current wording implies it's like just RUSAGE_SELF.
Compare:
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>
void copy() {
char buf[1024];
int fd = open("/proc/self/io", 0);
write(1, buf, read(fd, buf, sizeof(buf)));
close(fd);
}
int main() {
copy();
copy();
if (!fork()) {
zero:;
int fd = open("/dev/zero", 0);
char buf[64 * 1024] = {};
write(1, buf, 10000);
for (int i = 0; i < 1000; ++i)
read(fd, buf, sizeof(buf));
_exit(0);
}
sleep(1);
copy();
wait(NULL);
copy();
signal(SIGCHLD, SIG_IGN);
if (!fork())
goto zero;
sleep(1);
copy();
wait(NULL);
copy();
}
yielding
rchar: 3980
wchar: 0
syscr: 9
syscw: 0
read_bytes: 2968
write_bytes: 0
cancelled_write_bytes: 0
rchar: 4076
wchar: 96
syscr: 10
syscw: 1
read_bytes: 2968
write_bytes: 96
cancelled_write_bytes: 0
rchar: 4175
wchar: 195
syscr: 11
syscw: 2
read_bytes: 2968
write_bytes: 195
cancelled_write_bytes: 0
rchar: 65540276
wchar: 10296
syscr: 1012
syscw: 4
read_bytes: 2968
write_bytes: 10296
cancelled_write_bytes: 0
rchar: 65540387
wchar: 10407
syscr: 1013
syscw: 5
read_bytes: 2968
write_bytes: 10407
cancelled_write_bytes: 0
rchar: 65540498
wchar: 10518
syscr: 1014
syscw: 6
read_bytes: 2968
write_bytes: 10518
cancelled_write_bytes: 0
Just s/process/& and its waited-for children/ but re-broken per review.
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@xxxxxxxxxxxxxxxxxx>
---
man5/proc_pid_io.5 | 27 ++++++++++++++++++---------
1 file changed, 18 insertions(+), 9 deletions(-)
diff --git a/man5/proc_pid_io.5 b/man5/proc_pid_io.5
index d6eaebf5d..dc75a91de 100644
--- a/man5/proc_pid_io.5
+++ b/man5/proc_pid_io.5
@@ -11,7 +11,9 @@ .SH DESCRIPTION
.TP
.IR /proc/ pid /io " (since Linux 2.6.20)"
.\" commit 7c3ab7381e79dfc7db14a67c6f4f3285664e1ec2
-This file contains I/O statistics for the process, for example:
+This file contains I/O statistics
+for the process and its waited-for children,
+for example:
.IP
.in +4n
.EX
@@ -30,7 +32,9 @@ .SH DESCRIPTION
.RS
.TP
.IR rchar ": characters read"
-The number of bytes which this task has caused to be read from storage.
+The number of bytes
+which this task and its waited-for children
+have 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.
@@ -40,8 +44,9 @@ .SH DESCRIPTION
pagecache).
.TP
.IR wchar ": characters written"
-The number of bytes which this task has caused, or shall cause to be written
-to disk.
+The number of bytes
+which this task and its waited-for children
+have caused, or shall cause to be written to disk.
Similar caveats apply here as with
.IR rchar .
.TP
@@ -60,20 +65,24 @@ .SH DESCRIPTION
.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.
+Attempt to count the number of bytes
+which this process and its waited-for children
+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.
+Attempt to count the number of bytes
+which this process and its waited-for children
+caused to be sent to the storage layer.
.TP
.IR cancelled_write_bytes :
The big inaccuracy here is truncate.
If a process writes 1 MB to a file and then deletes the file,
it will in fact perform no writeout.
But it will have been accounted as having caused 1 MB of write.
-In other words: this field represents the number of bytes which this process
+In other words:
+this field represents the number of bytes
+which this process and its waited-for children
caused to not happen, by truncating pagecache.
A task can cause "negative" I/O too.
If this task truncates some dirty pagecache,
--
2.39.2
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