Fix pagetypeinfo behavior (#39985)

* fix pagetypeinfo behavior

* add changelog

* linter

CHANGELOG.next.asciidoc

@@ -163,6 +163,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - Fix issue where beats may report incorrect metrics for its own process when running inside a container {pull}39627[39627]
 - Fix for MySQL/Performance - Query failure for MySQL versions below v8.0.1, for performance metric `quantile_95`. {pull}38710[38710]
 - Normalize AWS RDS CPU Utilization values before making the metadata API call. {pull}39664[39664]
+- Fix behavior of pagetypeinfo metrics {pull}39985[39985]
 - Fix query logic for temp and non-temp tablespaces in Oracle module. {issue}38051[38051] {pull}39787[39787]
 
 *Osquerybeat*

metricbeat/module/linux/pageinfo/_meta/docs.asciidoc

@@ -1,4 +1,4 @@
-The pageinfo metricset reports on paging statistics as found in /proc/pagetypeinfo
+The pageinfo metricset reports on paging statistics as found in `/proc/pagetypeinfo`
 
 
 Reported metrics are broken down by page type: DMA, DMA32, Normal, and Highmem. These types are further broken down by order, which represents zones of 2^ORDER*PAGE_SIZE.
@@ -7,3 +7,4 @@ These metrics are divided into two reporting types: `buddyinfo`, which is summar
 
 This information can be used to determine memory fragmentation. The kernel https://www.kernel.org/doc/gorman/html/understand/understand009.html[buddy algorithim] will always search for the smallest page order to allocate, and if none is available, a larger page order will be split into two "buddies." When memory is freed, the kernel will attempt to merge the "buddies." If the only available pages are at lower orders, this indicates fragmentation, as buddy pages cannot be merged.
 
+Note that page counts from `/proc/pagetypeinfo` will only display values up to 100,000.

metricbeat/module/linux/pageinfo/pageinfo.go

@@ -24,6 +24,7 @@ import (
 
 	"github.com/elastic/beats/v7/libbeat/common/cfgwarn"
 	"github.com/elastic/beats/v7/metricbeat/mb"
+	"github.com/elastic/elastic-agent-libs/logp"
 	"github.com/elastic/elastic-agent-libs/mapstr"
 	"github.com/elastic/elastic-agent-system-metrics/metric/system/resolve"
 )
@@ -43,6 +44,7 @@ func init() {
 type MetricSet struct {
 	mb.BaseMetricSet
 	mod resolve.Resolver
+	log *logp.Logger
 }
 
 // New creates a new instance of the MetricSet. New is responsible for unpacking
@@ -55,6 +57,7 @@ func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
 	return &MetricSet{
 		BaseMetricSet: base,
 		mod:           sys,
+		log:           logp.NewLogger("pageinfo"),
 	}, nil
 }
 
@@ -72,7 +75,7 @@ func (m *MetricSet) Fetch(report mb.ReporterV2) error {
 
 	reader := bufio.NewReader(fd)
 
-	zones, err := readPageFile(reader)
+	zones, err := readPageFile(m.log, reader)
 	if err != nil {
 		return fmt.Errorf("error reading pagetypeinfo: %w", err)
 	}

metricbeat/module/linux/pageinfo/pageinfo_test.go

@@ -18,15 +18,30 @@
 package pageinfo
 
 import (
+	"bufio"
+	"os"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	mbtest "github.com/elastic/beats/v7/metricbeat/mb/testing"
 	_ "github.com/elastic/beats/v7/metricbeat/module/linux"
+	"github.com/elastic/elastic-agent-libs/logp"
 	"github.com/elastic/elastic-agent-libs/mapstr"
 )
 
+func TestFileRead(t *testing.T) {
+	fd, err := os.Open("./testdata/pagetypeinfo")
+	require.NoError(t, err)
+
+	reader := bufio.NewReader(fd)
+
+	zones, err := readPageFile(logp.L(), reader)
+	require.NoError(t, err)
+	require.Equal(t, int64(100000), zones.Zones[0].Normal["Movable"][1])
+}
+
 func TestData(t *testing.T) {
 	f := mbtest.NewReportingMetricSetV2Error(t, getConfig())
 	err := mbtest.WriteEventsReporterV2Error(f, t, ".")

metricbeat/module/linux/pageinfo/reader.go

@@ -19,10 +19,14 @@ package pageinfo
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
 	"io"
 	"regexp"
 	"strconv"
+	"strings"
+
+	"github.com/elastic/elastic-agent-libs/logp"
 )
 
 // zones represents raw pagetypeinfo data
@@ -46,11 +50,28 @@ type pageInfo struct {
 	Zones     map[int64]zones
 }
 
-var pageinfoLine = regexp.MustCompile(`Node\s*(\d), zone\s*([a-zA-z0-9]*), type\s*([a-zA-z0-9]*)\s*(\d*)\s*(\d*)\s*(\d*)\s*(\d*)\s*(\d*)\s*(\d*)\s*(\d*)\s*(\d*)\s*(\d*)\s*(\d*)\s*(\d*)`)
+var pageinfoLine = regexp.MustCompile(`Node\s*(\d), zone\s*([a-zA-z0-9]*), type\s*([a-zA-z0-9]*)\s*(>?\d*)\s*(>?\d*)\s*(>?\d*)\s*(>?\d*)\s*(>?\d*)\s*(>?\d*)\s*(>?\d*)\s*(>?\d*)\s*(>?\d*)\s*(>?\d*)\s*(>?\d*)`)
 
 // readPageFile reads a PageTypeInfo file and returns the parsed data
 // This returns a massive representation of all the meaningful data in /proc/pagetypeinfo
-func readPageFile(reader *bufio.Reader) (pageInfo, error) {
+//
+// the actual numbers in pagetypeinfo follow the same format as /proc/buddyinfo,
+// but broken down by node and ability to move
+// see https://www.kernel.org/doc/Documentation/filesystems/proc.txt:
+/*
+> cat /proc/buddyinfo
+
+Node 0, zone      DMA      0      4      5      4      4      3 ...
+Node 0, zone   Normal      1      0      0      1    101      8 ...
+Node 0, zone  HighMem      2      0      0      1      1      0 ...
+
+Each column represents the number of pages of a certain order which are
+available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
+ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
+available in ZONE_NORMAL, etc...
+*/
+
+func readPageFile(log *logp.Logger, reader *bufio.Reader) (pageInfo, error) {
 	nodes := make(map[int64]zones)
 
 	buddy := buddyInfo{
@@ -62,7 +83,7 @@ func readPageFile(reader *bufio.Reader) (pageInfo, error) {
 	for {
 		raw, err := reader.ReadString('\n')
 
-		if err == io.EOF || err == io.ErrUnexpectedEOF {
+		if errors.Is(err, io.EOF) || errors.Is(err, io.ErrUnexpectedEOF) {
 			break
 		}
 
@@ -97,9 +118,28 @@ func readPageFile(reader *bufio.Reader) (pageInfo, error) {
 		migrateType = string(match[3])
 		//Iterate over the order counts
 		for order, count := range match[4:] {
-			zoneOrders[order], err = strconv.ParseInt(string(count), 10, 64)
+			// zone count will produce numbers like this:
+			// >100000
+			// we need to catch that.
+			// for more context on why this happens, see the comment in mm/vmstat.c:
+			/*
+			 * Cap the free_list iteration because it might
+			 * be really large and we are under a spinlock
+			 * so a long time spent here could trigger a
+			 * hard lockup detector. Anyway this is a
+			 * debugging tool so knowing there is a handful
+			 * of pages of this order should be more than
+			 * sufficient.
+			 */
+			strCount := string(count)
+			if strings.Contains(strCount, ">") {
+				log.Debugf("got imprecise value '%s' in node %d", strCount, nodeLevel)
+				// make no assumptions, trim the value and pass it on
+				strCount = strings.Trim(strCount, ">")
+			}
+			zoneOrders[order], err = strconv.ParseInt(strCount, 10, 64)
 			if err != nil {
-				return pageInfo{}, fmt.Errorf("error parsing zone: %s: %w", string(count), err)
+				return pageInfo{}, fmt.Errorf("error parsing zone: %s: %w", strCount, err)
 			}
 			nodes[nodeLevel].OrderSummary[order] += zoneOrders[order]
 			if zoneType == "DMA" {

metricbeat/module/linux/pageinfo/testdata/pagetypeinfo

@@ -0,0 +1,24 @@
+Page block order: 9
+Pages per block:  512
+
+Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
+Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      0      0      0
+Node    0, zone      DMA, type      Movable      0      0      0      0      0      0      0      0      0      1      2
+Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
+Node    0, zone      DMA, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0
+Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
+Node    0, zone    DMA32, type    Unmovable    475    434    197    179     68     32     16     12     10      0      0
+Node    0, zone    DMA32, type      Movable  12157   6536   1695    225     79     49    379     88     28      1      0
+Node    0, zone    DMA32, type  Reclaimable    191     92    537    141     12      1      1      1      1      0      0
+Node    0, zone    DMA32, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0
+Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
+Node    0, zone   Normal, type    Unmovable     66    160    177     31     10     10      7      1      0      0      0
+Node    0, zone   Normal, type      Movable     10 >100000  70473   3338    115    109     14     60     55      1      0
+Node    0, zone   Normal, type  Reclaimable    994    603    162     16      1      0      0      0      0      0      0
+Node    0, zone   Normal, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0
+Node    0, zone   Normal, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
+
+Number of blocks type     Unmovable      Movable  Reclaimable   HighAtomic      Isolate
+Node 0, zone      DMA            3            5            0            0            0
+Node 0, zone    DMA32           29         1405           94            0            0
+Node 0, zone   Normal          841        29689          702            0            0