Two additions:
(E) Indicates "THP_enabled: 0" in /proc/pid/status only if THPs are not
disabled completely
As raised off-list, this should be "only if THPs are disabled completely"
Only indicating that THPs are disabled when they are really disabled
completely, not only partially.
> > The documented semantics in the man page for PR_SET_THP_DISABLE
"is inherited by a child created via fork(2) and is preserved across
execve(2)" is maintained. This behavior, for example, allows for
disabling THPs for a workload through the launching process (e.g.,
systemd where we fork() a helper process to then exec()).
There is currently not way to prevent that a process will not issue
PR_SET_THP_DISABLE itself to re-enable THP. We could add a "seal" option
to PR_SET_THP_DISABLE through another flag if ever required. The known
users (such as redis) really use PR_SET_THP_DISABLE to disable THPs, so
that is not added for now.
I don't think there is any user that would try re-enabling THPs through
that interface. It's kind-of against the original purpose (man page):
"Setting this flag provides a method for disabling transparent huge
pages for jobs where the code cannot be modified ..."
So if ever really required, one could investigate forbidding re-enabling
once disabled. But that obviously needs more investigation.
(also, if a workload ever enables THPs through that mechanism, probably
it is to blame)
--
Cheers,
David / dhildenb
