Lot of jobs do not discard their build history which is filling up the disk on gallium (T91211). Most of the jobs should have a day based logrotation ie in jjb:
logrotate: daysToKeep: 30
Example of top offenders:
cd /var/lib/jenkins/jobs $ stat --format '%h:%n' */builds|sort -rn|head -n30 13371:operations-puppet-tox-data_admin_lint/builds 12284:mwext-Wikibase-lint/builds 10051:mwext-MobileFrontend-lint/builds 8989:mwext-MobileFrontend-qunit/builds 8983:mwext-MobileFrontend-qunit-mobile/builds 8821:mwext-Flow-lint/builds 8713:operations-apache-config-lint/builds 7512:mwext-VisualEditor-lint/builds 7003:mwext-VisualEditor-npm/builds 7002:mwext-VisualEditor-qunit/builds 6991:mwext-VisualEditor-doc-test/builds 6932:operations-mw-config-tests/builds 5672:mwext-Wikibase-qunit/builds 5656:mwext-Wikibase-repo-tests/builds 5653:mwext-Wikibase-repo-api-tests/builds 5642:mwext-Wikibase-client-tests/builds 5618:mediawiki-core-doxygen-publish/builds 5463:mediawiki-gate/builds 5353:VisualEditor-npm/builds 5096:pywikibot-core-tox-flake8/builds 5040:mediawiki-core-phplint/builds 4863:operations-puppet-validate/builds 4777:VisualEditor-jsduck/builds 4638:mediawiki-core-bundle-rubocop/builds 4422:mwext-Flow-qunit/builds 4384:mwext-MobileFrontend-phpcs-HEAD/builds 4263:mediawiki-core-regression-phpcs-HEAD/builds 3953:pywikibot-core-tox-nose/builds 3920:mwext-MobileFrontend-jslint/builds 3808:operations-puppet-puppetlint-strict/builds