diff --git a/doc/administration/monitoring/prometheus/gitlab_metrics.md b/doc/administration/monitoring/prometheus/gitlab_metrics.md
index 4f8fbd0c07e227cc9936b8657a8cb4677317f0c2..b19b342c665b4436e435b813dae5b98fc969ded5 100644
--- a/doc/administration/monitoring/prometheus/gitlab_metrics.md
+++ b/doc/administration/monitoring/prometheus/gitlab_metrics.md
@@ -347,6 +347,7 @@ Some basic Ruby runtime metrics are available:
|:---------------------------------------- |:--------- |:----- |:----------- |
| `ruby_gc_duration_seconds` | Counter | 11.1 | Time spent by Ruby in GC |
| `ruby_gc_stat_...` | Gauge | 11.1 | Various metrics from [GC.stat](https://ruby-doc.org/core-2.6.5/GC.html#method-c-stat) |
+| `ruby_gc_stat_ext_heap_fragmentation` | Gauge | 15.2 | Degree of Ruby heap fragmentation as live objects versus eden slots (range 0 to 1) |
| `ruby_file_descriptors` | Gauge | 11.1 | File descriptors per process |
| `ruby_sampler_duration_seconds` | Counter | 11.1 | Time spent collecting stats |
| `ruby_process_cpu_seconds_total` | Gauge | 12.0 | Total amount of CPU time per process |
diff --git a/lib/gitlab/metrics/memory.rb b/lib/gitlab/metrics/memory.rb
new file mode 100644
index 0000000000000000000000000000000000000000..c165cdec7a3ddb9b17bce0e6f7a35f1889d2d6eb
--- /dev/null
+++ b/lib/gitlab/metrics/memory.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module Gitlab
+ module Metrics
+ module Memory
+ extend self
+
+ HEAP_SLOTS_PER_PAGE = GC::INTERNAL_CONSTANTS[:HEAP_PAGE_OBJ_LIMIT]
+
+ def gc_heap_fragmentation(gc_stat = GC.stat)
+ 1 - (gc_stat[:heap_live_slots] / (HEAP_SLOTS_PER_PAGE * gc_stat[:heap_eden_pages].to_f))
+ end
+ end
+ end
+end
diff --git a/lib/gitlab/metrics/samplers/ruby_sampler.rb b/lib/gitlab/metrics/samplers/ruby_sampler.rb
index 4a3ef3711a508e0f59db7449a6555b6f1e513cb3..8e0022933471c2996197402869b6c4e9226c017d 100644
--- a/lib/gitlab/metrics/samplers/ruby_sampler.rb
+++ b/lib/gitlab/metrics/samplers/ruby_sampler.rb
@@ -39,7 +39,8 @@ def init_metrics
process_proportional_memory_bytes: ::Gitlab::Metrics.gauge(metric_name(:process, :proportional_memory_bytes), 'Memory used (PSS)', labels),
process_start_time_seconds: ::Gitlab::Metrics.gauge(metric_name(:process, :start_time_seconds), 'Process start time seconds'),
sampler_duration: ::Gitlab::Metrics.counter(metric_name(:sampler, :duration_seconds_total), 'Sampler time', labels),
- gc_duration_seconds: ::Gitlab::Metrics.histogram(metric_name(:gc, :duration_seconds), 'GC time', labels, GC_REPORT_BUCKETS)
+ gc_duration_seconds: ::Gitlab::Metrics.histogram(metric_name(:gc, :duration_seconds), 'GC time', labels, GC_REPORT_BUCKETS),
+ heap_fragmentation: ::Gitlab::Metrics.gauge(metric_name(:gc_stat_ext, :heap_fragmentation), 'Ruby heap fragmentation', labels)
}
GC.stat.keys.each do |key|
@@ -76,8 +77,13 @@ def sample_gc
end
# Collect generic GC stats
- GC.stat.each do |key, value|
- metrics[key].set(labels, value)
+ GC.stat.then do |gc_stat|
+ gc_stat.each do |key, value|
+ metrics[key].set(labels, value)
+ end
+
+ # Collect custom GC stats
+ metrics[:heap_fragmentation].set(labels, Memory.gc_heap_fragmentation(gc_stat))
end
end
diff --git a/metrics_server/dependencies.rb b/metrics_server/dependencies.rb
index 3f188658ba298b58fc694019d6579eb7d5e9bb22..233511eb505e4f11b3267ddcd67db166bf18e218 100644
--- a/metrics_server/dependencies.rb
+++ b/metrics_server/dependencies.rb
@@ -20,6 +20,7 @@
require_relative '../lib/gitlab/metrics/prometheus'
require_relative '../lib/gitlab/metrics'
require_relative '../lib/gitlab/metrics/system'
+require_relative '../lib/gitlab/metrics/memory'
require_relative '../lib/gitlab/metrics/samplers/base_sampler'
require_relative '../lib/gitlab/metrics/samplers/ruby_sampler'
require_relative '../lib/gitlab/metrics/exporter/base_exporter'
diff --git a/spec/lib/gitlab/metrics/memory_spec.rb b/spec/lib/gitlab/metrics/memory_spec.rb
new file mode 100644
index 0000000000000000000000000000000000000000..fd8ca3b37c634eb56047f6ad9160b18ca90bf217
--- /dev/null
+++ b/spec/lib/gitlab/metrics/memory_spec.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+require 'fast_spec_helper'
+
+RSpec.describe Gitlab::Metrics::Memory do
+ describe '.gc_heap_fragmentation' do
+ subject(:call) do
+ described_class.gc_heap_fragmentation(
+ heap_live_slots: gc_stat_heap_live_slots,
+ heap_eden_pages: gc_stat_heap_eden_pages
+ )
+ end
+
+ context 'when the Ruby heap is perfectly utilized' do
+ # All objects are located in a single heap page.
+ let(:gc_stat_heap_live_slots) { described_class::HEAP_SLOTS_PER_PAGE }
+ let(:gc_stat_heap_eden_pages) { 1 }
+
+ it { is_expected.to eq(0) }
+ end
+
+ context 'when the Ruby heap is greatly fragmented' do
+ # There is one object per heap page.
+ let(:gc_stat_heap_live_slots) { described_class::HEAP_SLOTS_PER_PAGE }
+ let(:gc_stat_heap_eden_pages) { described_class::HEAP_SLOTS_PER_PAGE }
+
+ # The heap can never be "perfectly fragmented" because that would require
+ # zero objects per page.
+ it { is_expected.to be > 0.99 }
+ end
+
+ context 'when the Ruby heap is semi-fragmented' do
+ # All objects are spread over two pages i.e. each page is 50% utilized.
+ let(:gc_stat_heap_live_slots) { described_class::HEAP_SLOTS_PER_PAGE }
+ let(:gc_stat_heap_eden_pages) { 2 }
+
+ it { is_expected.to eq(0.5) }
+ end
+ end
+end
diff --git a/spec/lib/gitlab/metrics/samplers/ruby_sampler_spec.rb b/spec/lib/gitlab/metrics/samplers/ruby_sampler_spec.rb
index dfae5aa678450ace8f64d3a459a1a543389ab7f9..b1566ffa7b4603618c046be1f31b78322f1e232e 100644
--- a/spec/lib/gitlab/metrics/samplers/ruby_sampler_spec.rb
+++ b/spec/lib/gitlab/metrics/samplers/ruby_sampler_spec.rb
@@ -125,5 +125,11 @@
sampler.sample
end
+
+ it 'adds a heap fragmentation metric' do
+ expect(sampler.metrics[:heap_fragmentation]).to receive(:set).with({}, anything)
+
+ sampler.sample
+ end
end
end