On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:

This patch series will free some vmemmap pages(struct page structures)
associated with each hugetlbpage when preallocated to save memory.

It would be lovely to be able to do this.  Unfortunately, it's completely
impossible right now.  Consider, for example, get_user_pages() called
on the fifth page of a hugetlb page.

I've spent a lot of time thinking about this, and there's a lot of work
that needs to happen before we can do this, mostly in device drivers.
Do you want to help?  It's a multi-year project.