On Wed,  7 Aug 2019 13:15:54 -0400 "Joel Fernandes (Google)" [off-list ref] wrote:

In Android, we are using this for the heap profiler (heapprofd) which
profiles and pin points code paths which allocates and leaves memory
idle for long periods of time. This method solves the security issue
with userspace learning the PFN, and while at it is also shown to yield
better results than the pagemap lookup, the theory being that the window
where the address space can change is reduced by eliminating the
intermediate pagemap look up stage. In virtual address indexing, the
process's mmap_sem is held for the duration of the access.

So is heapprofd a developer-only thing?  Is heapprofd included in
end-user android loads?  If not then, again, wouldn't it be better to
make the feature Kconfigurable so that Android developers can enable it
during development then disable it for production kernels?