On 07/30/13 17:24, Peter Schiffer wrote: > Attempt to document fields in the /proc/[pid]/io file, based on the > Documentation/filesystems/proc.txt. The text will probably need some > grammar corrections. Hi Peter, Thanks for the patch. But, not that your mailer munged the patch, so I had to fix by hand. I've applied it. Thanks, Michael > Signed-off-by: Peter Schiffer <pschiffe@xxxxxxxxxx> > --- > man5/proc.5 | 95 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 91 insertions(+), 4 deletions(-) > > diff --git a/man5/proc.5 b/man5/proc.5 > index 375a131..6fd4543 100644 > --- a/man5/proc.5 > +++ b/man5/proc.5 > @@ -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 2013-07-30 "Linux" "Linux Programmer's Manual" > .SH NAME > proc \- process information pseudo-file system > .SH DESCRIPTION > @@ -350,9 +350,96 @@ file access mode and file status flags (see > .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)" > +This file contains IO statistics for each running 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 > +.IP * 2 > +.IR rchar : > +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 > +.BR read (2) > +and > +.BR pread (2). > +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). > +.IP * > +.IR wchar : > +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 > +.IR rchar . > +.IP * > +.IR syscr : > +read syscalls > + > +Attempt to count the number of read I/O operations, i.e. syscalls like > +.BR read (2) > +and > +.BR pread (2). > +.IP * > +.IR syscw : > +write syscalls > + > +Attempt to count the number of write I/O operations, i.e. syscalls like > +.BR write (2) > +and > +.BR pwrite (2). > +.IP * > +.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. > +.IP * > +.IR write_bytes : > +bytes written > + > +Attempt to count the number of bytes which this process caused to be > sent to > +the storage layer. > +.IP * > +.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 number of bytes which this process > +caused to not happen, by truncating pagecache. > +A task can cause "negative" IO too. > +If this task truncates some dirty pagecache, > +some IO which another task has been accounted for > +(in its write_bytes) will not be happening. > +.IP > +.IR Note : > + > +At its current implementation state, this is 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 those 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
