On Mon 23-05-22 17:18:32, Zach O'Keefe wrote:
[...]
> Idea: MADV_COLLAPSE should respect VM_NOHUGEPAGE and "never" THP mode,
> but otherwise would attempt to collapse.
I do agree that {process_}madvise should fail on VM_NOHUGEPAGE. The
process has explicitly noted that THP shouldn't be used on such a VMA
and seeing THP could be observed as not complying with that contract.
I am not so sure about the global "never" policy, though. The global
policy controls _kernel_ driven THPs. As the request to collapse memory
comes from the userspace I do not think it should be limited by the
kernel policy. I also think it can be beneficial to implement userspace
based THP policies and exclude any kernel interference and that could be
achieved by global kernel "never" policy and implement the whole
functionality by process_madvise.
--
Michal Hocko
SUSE Labs
