HHVM 3.7.1 logs following errors:
```
-> ERROR 8: Undefined index: num_seg at [/opt/phabricator/phabricator/src/applications/cache/spec/PhabricatorDataCacheSpec.php:77]
arcanist(head=master, ref.master=9a7c4d87a850), libphremoteuser(head=master, ref.master=1def4e2d7f07), phabricator(head=master, ref.master=ee11587c19c7), phutil(head=master, ref.master=3b4da3f33153), sprint(head=master, ref.master=ba0d4c2d46da)
#0 PhabricatorDataCacheSpec::initAPCCommonSpec() called at [<phabricator>/src/applications/cache/spec/PhabricatorDataCacheSpec.php:38]
#1 PhabricatorDataCacheSpec::initAPCSpec() called at [<phabricator>/src/applications/cache/spec/PhabricatorDataCacheSpec.php:21]
#2 PhabricatorDataCacheSpec::getActiveCacheSpec() called at [<phabricator>/src/applications/config/check/PhabricatorCacheSetupCheck.php:11]
#3 PhabricatorCacheSetupCheck::executeChecks() called at [<phabricator>/src/applications/config/check/PhabricatorSetupCheck.php:45]
#4 PhabricatorSetupCheck::runSetupChecks() called at [<phabricator>/src/applications/config/check/PhabricatorSetupCheck.php:133]
#5 PhabricatorSetupCheck::runAllChecks() called at [<phabricator>/src/applications/config/check/PhabricatorSetupCheck.php:91]
#6 PhabricatorSetupCheck::willProcessRequest() called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:94]
#7 AphrontApplicationConfiguration::runHTTPRequest() called at [<phabricator>/webroot/index.php:21]
-> ERROR 8: Undefined index: seg_size at [/opt/phabricator/phabricator/src/applications/cache/spec/PhabricatorDataCacheSpec.php:77]
arcanist(head=master, ref.master=9a7c4d87a850), libphremoteuser(head=master, ref.master=1def4e2d7f07), phabricator(head=master, ref.master=ee11587c19c7), phutil(head=master, ref.master=3b4da3f33153), sprint(head=master, ref.master=ba0d4c2d46da)
#0 PhabricatorDataCacheSpec::initAPCCommonSpec() called at [<phabricator>/src/applications/cache/spec/PhabricatorDataCacheSpec.php:38]
#1 PhabricatorDataCacheSpec::initAPCSpec() called at [<phabricator>/src/applications/cache/spec/PhabricatorDataCacheSpec.php:21]
#2 PhabricatorDataCacheSpec::getActiveCacheSpec() called at [<phabricator>/src/applications/config/check/PhabricatorCacheSetupCheck.php:11]
#3 PhabricatorCacheSetupCheck::executeChecks() called at [<phabricator>/src/applications/config/check/PhabricatorSetupCheck.php:45]
#4 PhabricatorSetupCheck::runSetupChecks() called at [<phabricator>/src/applications/config/check/PhabricatorSetupCheck.php:133]
#5 PhabricatorSetupCheck::runAllChecks() called at [<phabricator>/src/applications/config/check/PhabricatorSetupCheck.php:91]
#6 PhabricatorSetupCheck::willProcessRequest() called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:94]
#7 AphrontApplicationConfiguration::runHTTPRequest() called at [<phabricator>/webroot/index.php:21]
-> ERROR 8: Undefined index: mem_size at [/opt/phabricator/phabricator/src/applications/cache/spec/PhabricatorDataCacheSpec.php:80]
arcanist(head=master, ref.master=9a7c4d87a850), libphremoteuser(head=master, ref.master=1def4e2d7f07), phabricator(head=master, ref.master=ee11587c19c7), phutil(head=master, ref.master=3b4da3f33153), sprint(head=master, ref.master=ba0d4c2d46da)
#0 PhabricatorDataCacheSpec::initAPCCommonSpec() called at [<phabricator>/src/applications/cache/spec/PhabricatorDataCacheSpec.php:38]
#1 PhabricatorDataCacheSpec::initAPCSpec() called at [<phabricator>/src/applications/cache/spec/PhabricatorDataCacheSpec.php:21]
#2 PhabricatorDataCacheSpec::getActiveCacheSpec() called at [<phabricator>/src/applications/config/check/PhabricatorCacheSetupCheck.php:11]
#3 PhabricatorCacheSetupCheck::executeChecks() called at [<phabricator>/src/applications/config/check/PhabricatorSetupCheck.php:45]
#4 PhabricatorSetupCheck::runSetupChecks() called at [<phabricator>/src/applications/config/check/PhabricatorSetupCheck.php:133]
#5 PhabricatorSetupCheck::runAllChecks() called at [<phabricator>/src/applications/config/check/PhabricatorSetupCheck.php:91]
#6 PhabricatorSetupCheck::willProcessRequest() called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:94]
#7 AphrontApplicationConfiguration::runHTTPRequest() called at [<phabricator>/webroot/index.php:21]
```