Sys::Statistics::Linux::PgSwStats - Collect linux paging and swapping statistics.

    use Sys::Statistics::Linux::PgSwStats;

    my $lxs = Sys::Statistics::Linux::PgSwStats->new;
    $lxs->init;
    sleep 1;
    my $stat = $lxs->get;

    my $lxs = Sys::Statistics::Linux::PgSwStats->new(initfile => $file);
    $lxs->init;
    my $stat = $lxs->get;

    pgpgin      -  Number of pages the system has paged in from disk per second.
    pgpgout     -  Number of pages the system has paged out to disk per second.
    pswpin      -  Number of pages the system has swapped in from disk per second.
    pswpout     -  Number of pages the system has swapped out to disk per second.

    The following statistics are only available by kernels from 2.6.

    pgfault     -  Number of page faults the system has made per second (minor + major).
    pgmajfault  -  Number of major faults per second the system required loading a memory page from disk.

    my $lxs = Sys::Statistics::Linux::PgSwStats->new;

    my $lxs = Sys::Statistics::Linux::PgSwStats->new(initfile => '/tmp/pgswstats.yml');

     Sys::Statistics::Linux::PgSwStats->new(
        files => {
            # This is the default
            path   => '/proc',
            stat   => 'stat',
            vmstat => 'vmstat',
        }
    );

    $lxs->init;

    my $stat = $lxs->get;

package Sys::Statistics::Linux::PgSwStats;

use strict;
use warnings;
use Carp qw(croak);
use Time::HiRes;

our $VERSION = '0.18';

sub new {
    my $class = shift;
    my $opts  = ref($_[0]) ? shift : {@_};

    my %self = (
        files => {
            path   => '/proc',
            stat   => 'stat',
            vmstat => 'vmstat',
        }
    );

    if (defined $opts->{initfile}) {
        require YAML::Syck;
        $self{initfile} = $opts->{initfile};
    }

    foreach my $file (keys %{ $opts->{files} }) {
        $self{files}{$file} = $opts->{files}->{$file};
    }

    return bless \%self, $class;
}

sub init {
    my $self = shift;

    if ($self->{initfile} && -r $self->{initfile}) {
        $self->{init} = YAML::Syck::LoadFile($self->{initfile});
        $self->{time} = delete $self->{init}->{time};
    } else {
        $self->{time} = Time::HiRes::gettimeofday();
        $self->{init} = $self->_load;
    }
}

sub get {
    my $self  = shift;
    my $class = ref $self;

    if (!exists $self->{init}) {
        croak "$class: there are no initial statistics defined";
    }

    $self->{stats} = $self->_load;
    $self->_deltas;

    if ($self->{initfile}) {
        $self->{init}->{time} = $self->{time};
        YAML::Syck::DumpFile($self->{initfile}, $self->{init});
    }

    return $self->{stats};
}

sub raw {
    my $self = shift;
    my $stat = $self->_load;

    return $stat;
}

#
# private stuff
#

sub _load {
    my $self  = shift;
    my $class = ref $self;
    my $file  = $self->{files};
    my %stats = ();

    my $filename = $file->{path} ? "$file->{path}/$file->{stat}" : $file->{stat};
    open my $fh, '<', $filename or croak "$class: unable to open $filename ($!)";

    while (my $line = <$fh>) {
        if ($line =~ /^page\s+(\d+)\s+(\d+)$/) {
            @stats{qw(pgpgin pgpgout)} = ($1, $2);
        } elsif ($line =~ /^swap\s+(\d+)\s+(\d+)$/) {
            @stats{qw(pswpin pswpout)} = ($1, $2);
        }
    }

    close($fh);

    # if paging and swapping are not found in /proc/stat
    # then let's try a look into /proc/vmstat (since 2.6)

    if (!defined $stats{pswpout}) {
        my $filename = $file->{path} ? "$file->{path}/$file->{vmstat}" : $file->{vmstat};
        open my $fh, '<', $filename or croak "$class: unable to open $filename ($!)";
        while (my $line = <$fh>) {
            next unless $line =~ /^(pgpgin|pgpgout|pswpin|pswpout|pgfault|pgmajfault)\s+(\d+)/;
            $stats{$1} = $2;
        }
        close($fh);
    }

    return \%stats;
}

sub _deltas {
    my $self  = shift;
    my $class = ref $self;
    my $istat = $self->{init};
    my $lstat = $self->{stats};
    my $time  = Time::HiRes::gettimeofday();
    my $delta = sprintf('%.2f', $time - $self->{time});
    $self->{time} = $time;

    while (my ($k, $v) = each %{$lstat}) {
        if (!defined $istat->{$k} || !defined $lstat->{$k}) {
            croak "$class: not defined key found '$k'";
        }

        if ($v !~ /^\d+\z/ || $istat->{$k} !~ /^\d+\z/) {
            croak "$class: invalid value for key '$k'";
        }

        if ($lstat->{$k} == $istat->{$k} || $istat->{$k} > $lstat->{$k}) {
            $lstat->{$k} = sprintf('%.2f', 0);
        } elsif ($delta > 0) {
            $lstat->{$k} = sprintf('%.2f', ($lstat->{$k} - $istat->{$k}) / $delta);
        } else {
            $lstat->{$k} = sprintf('%.2f', $lstat->{$k} - $istat->{$k});
        }

        $istat->{$k}  = $v;
    }
}

1;