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.\" This page Copyright (C) 1997 Joshua Yelon <jyelon@uiuc.edu>
.\" Distribution subject to the terms of the GPL.
.\" minor fixes by Bernd Eckenfels <ecki@debian.org> 1998-04-18
.\" minor fixes by Bernd Eckenfels <ecki@debian.org> 1998-11-01
.TH MEMSTAT 1 "01 November 1998 " "Debian" "Linux Programmer's Manual"
.SH NAME
memstat \- Identify what's using up virtual memory.
.SH SYNOPSIS
.ft B
.B memstat
.RB [ "\-w" ]
.br
.SH DESCRIPTION
\fBmemstat\fP lists all the processes, executables, and shared libraries
that are using up virtual memory.
First, the processes are listed. An amount of memory is shown along
with a process ID and the name of the executable which the process is
running. The amount of memory shown does not include shared memory:
it only includes memory which is private to that process. So, if a
process is using a shared library like libc, the memory used to hold
that library is not included. The memory used to hold the
executable's text-segment is also not included, since that too is
shareable.
After the processes, the shared objects are listed. An amount of
memory is shown along with the filename of the shared object, followed
by a list of the processes using the shared object.
Finally, a grand total is shown. Note that this program shows the
amount of \fBvirtual\fP (not real) memory used by the various items.
\fBmemstat\fP gets its input from the /proc filesystem. This must be
compiled into your kernel and mounted for \fBmemstat\fP to work. The
pathnames shown next to the shared objects are determined by scanning
the disk. \fBmemstat\fP uses a configuration file, /etc/memstat.conf,
to determine which directories to scan. This file should include all
the major bin and lib directories in your system, as well as the /dev
directory. If you run an executable which is not in one of these
directories, it will be listed by memstat as ``[0dev]:<inode>''.
.SS Options
The \fB-w\fP switch causes a wide printout: lines are not truncated at
80 columns.
.PP
.SH NOTES
These reports are intended to help identify programs that are using an
excessive amount of memory, and to reduce overall memory waste.
.PP
.SH FILES
.ta
.nf
/etc/memstat.conf
/proc/*/maps
.fi
.SH "SEE ALSO"
ps(1), top(1), free(1), vmstat(8), lsof(8), /usr/doc/memstat/memstat-tutorial.txt.gz
.PP
.SH BUGS
If you do the math, you'll see that ps and memstat don't always agree
about how much virtual memory a process is using. This is because
most processes seem to map certain shared pages twice. memstat counts
these pages once, ps counts them twice. I'm not sure which is
the ``right'' way to measure it.
The proc filesystem identifies files by their device number and inode
number. To be useful, these numbers must be translated back into
filenames. This requires searching the disk (and thus the awkward
configuration file memstst.conf). There should be some way around
this, perhaps by adding the dev/inode info to the locate db?
The stat system call returns a dev_t type, but the proc filesystem
contains a device readout in the form of a string. I have improvised
a routine to convert the device readout string into a dev_t, but I'm
not sure it will work on all architectures.
It is possible to confuse \fBmemstat\fP by using mmap in combination
with a block-device. In the original version, \fBmemstat\fP treated
block devices just like any other file, and if you mmap'ed one of
them, they would show up on the shared-object list. This worked for
mmap'ed hard disks and floppies, but it produced absurd results with
block devices like /dev/zero and /dev/mem. As a partial fix,
\fBmemstat\fP now ignores all mapped block devices, though this may
cause \fBmemstat\fP to ignore some memory usage.
We really ought to show some real-memory usage statistics, but it's
just not there in /proc.
Memory used by the kernel itself is not listed.
.SH AUTHOR
Written by Joshua Yelon <jyelon@uiuc.edu> and patched by Bernd Eckenfels
<ecki@debian.org>
|
