'\"macro stdmacro
.\"
.\" Copyright (c) 2014 Red Hat.
.\"
.\" This program is free software; you can redistribute it and/or modify it
.\" under the terms of the GNU General Public License as published by the
.\" Free Software Foundation; either version 2 of the License, or (at your
.\" option) any later version.
.\"
.\" This program is distributed in the hope that it will be useful, but
.\" WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
.\" or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
.\" for more details.
.\"
.\"
.TH PMDAZSWAP 1 "PCP" "Performance Co-Pilot"
.SH NAME
\f3pmdazswap\f1 \- zswap (compressed swap) PMDA
.SH DESCRIPTION
\f3pmdazswap\f1 is a Performance Metrics Domain Agent (PMDA) which exports
metric values about compressed swap operation, as tracked by the
.B zswap
Linux kernel module.
.PP
Zswap is a lightweight compressed cache for swap pages.
It takes pages that are in the process of being swapped out and attempts
to compress them into a dynamically allocated RAM-based memory pool.
Zswap trades CPU cycles for potentially reduced swap I/O.
This tradeoff can also result in a performance improvement if reads
from the compressed cache are faster than reads from a swap device.
.PP
This PMDA exports metrics about pool size, number of pages stored, and
various counters for the reasons pages are rejected.
.SH INSTALLATION
Install the zswap PMDA by using the Install script as root:
.sp 1
.RS +4
.ft B
.nf
# cd $PCP_PMDAS_DIR/zswap
# ./Install
.fi
.ft P
.RE
.sp 1
.PP
To uninstall, do the following as root:
.sp 1
.RS +4
.ft B
.nf
# cd $PCP_PMDAS_DIR/zswap
# ./Remove
.fi
.ft P
.RE
.sp 1
\fBpmdazswap\fR is launched by \fIpmcd\fR(1) and should never be executed
directly. The Install and Remove scripts notify \fIpmcd\fR(1) when the
agent is installed or removed.
.SH FILES
.IP "\fB$PCP_PMDAS_DIR/zswap/Install\fR" 4
installation script for the \fBpmdazswap\fR agent
.IP "\fB$PCP_PMDAS_DIR/zswap/Remove\fR" 4
undo installation script for the \fBpmdazswap\fR agent
.IP "\fB$PCP_LOG_DIR/pmcd/zswap.log\fR" 4
default log file for error messages from \fBpmdazswap\fR
.SH PCP ENVIRONMENT
Environment variables with the prefix \fBPCP_\fR are used to parameterize
the file and directory names used by \fBPCP\fR. On each installation, the
file \fB/etc/pcp.conf\fR contains the local values for these variables.
The \fB$PCP_CONF\fR variable may be used to specify an alternative
configuration file, as described in \fIpcp.conf\fR(5).
.SH SEE ALSO
.BR PCPIntro (1)
and
.BR pmcd (1).