Run static benchmarks from 'derailed_benchmarks'

Two static memory benchmarks will be included in our CI pipeline. It
will load gems from the Gemfile and check the amount of RAM consumed
as well as the number of objects allocated and retained.
Aggregated values will be included as 'metrics' into MRs while full
reports will be downloadable as job artifacts.

.gitlab-ci.yml

@@ -37,6 +37,7 @@ include:
   - local: .gitlab/ci/cng.gitlab-ci.yml
   - local: .gitlab/ci/docs.gitlab-ci.yml
   - local: .gitlab/ci/frontend.gitlab-ci.yml
+  - local: .gitlab/ci/memory.gitlab-ci.yml
   - local: .gitlab/ci/pages.gitlab-ci.yml
   - local: .gitlab/ci/qa.gitlab-ci.yml
   - local: .gitlab/ci/reports.gitlab-ci.yml

.gitlab/ci/memory.gitlab-ci.yml

@@ -0,0 +1,19 @@
+memory-static:
+  extends: .dedicated-no-docs-no-db-pull-cache-job
+  script:
+    # Uses two different reports from the 'derailed_benchmars' gem.
+
+    # Loads each of gems in the Gemfile and checks how much memory they consume when they are required.
+    # 'derailed_benchmarks' internally uses 'get_process_mem'
+    - scripts/memory-static 'tmp/memory_static_full_report.txt' 'tmp/memory_static_metrics.txt'
+
+    # Outputs detailed information about objects created while gems are loaded.
+    # 'derailed_benchmarks' internally uses 'memory_profiler'
+    - scripts/memory-static-objects 'tmp/memory_static_objects_full_report.txt' 'tmp/memory_static_metrics.txt'
+  artifacts:
+    paths:
+      - tmp/memory_static_full_report.txt
+      - tmp/memory_static_objects_full_report.txt
+      - tmp/memory_static_metrics.txt
+    reports:
+      metrics: tmp/memory_static_metrics.txt

scripts/memory-static

@@ -0,0 +1,20 @@
+#!/usr/bin/env ruby
+
+require_relative '../lib/gitlab/popen'
+
+full_report_filename, metrics_filename = ARGV
+abort 'usage: memory-static <full_report_filename> <metrics_filename>' unless full_report_filename && metrics_filename
+
+full_report, status = Gitlab::Popen.popen(%w(bundle exec derailed bundle:mem))
+abort 'failed to execute the benchmark' unless status.zero?
+
+File.open(full_report_filename, 'w') do |f|
+  f.write(full_report)
+end
+
+stats = /TOP: (?<total_mibs_str>.*) MiB/.match(full_report.lines.first)
+abort 'failed to process the benchmark output' unless stats
+
+File.open(metrics_filename, 'a') do |f|
+  f.puts "memory_static_total_mb #{stats[:total_mibs_str].to_f.round(1)}"
+end

scripts/memory-static-objects

@@ -0,0 +1,27 @@
+#!/usr/bin/env ruby
+
+require_relative '../lib/gitlab/popen'
+
+full_report_filename, metrics_filename = ARGV
+abort 'usage: memory-static-objects <full_report_filename> <metrics_filename>' unless full_report_filename && metrics_filename
+
+full_report, status = Gitlab::Popen.popen(%w(bundle exec derailed bundle:objects))
+abort 'failed to execute the benchmark' unless status.zero?
+
+File.open(full_report_filename, 'w') do |f|
+  f.write(full_report)
+end
+
+allocated_str = full_report.lines[1]
+retained_str = full_report.lines[2]
+allocated_stats = /Total allocated: (?<bytes>.*) bytes \((?<objects>.*) objects\)/.match(allocated_str)
+retained_stats = /Total retained: (?<bytes>.*) bytes \((?<objects>.*) objects\)/.match(retained_str)
+
+abort 'failed to process the benchmark output' unless allocated_stats && retained_stats
+
+File.open(metrics_filename, 'a') do |f|
+  f.puts "memory_static_objects_allocated_mb #{(allocated_stats[:bytes].to_f / (1024 * 1024)).round(1)}"
+  f.puts "memory_static_objects_retained_mb #{(retained_stats[:bytes].to_f / (104 * 1024)).round(1)}"
+  f.puts "memory_static_objects_allocated_items #{allocated_stats[:objects]}"
+  f.puts "memory_static_objects_retained_items #{retained_stats[:objects]}"
+end