On Tue, Aug 18, 2020 at 12:25 AM SeongJae Park [off-list ref] wrote:

From: SeongJae Park <redacted>

Changes from Previous Version
=============================

- Use 42 as the fake target id for paddr instead of -1
- Fix a typo

Introduction
============

DAMON[1] programming interface users can extend DAMON for any address space by
configuring the address-space specific low level primitives with appropriate
ones including their own implementations.  However, because the implementation
for the virtual address space is only available now, the users should implement
their own for other address spaces.  Worse yet, the user space users who rely
on the debugfs interface and user space tool, cannot implement their own.

This patchset implements another reference implementation of the low level
primitives for the physical memory address space.  With this change, hence, the
kernel space users can monitor both the virtual and the physical address spaces
by simply changing the configuration in the runtime.  Further, this patchset
links the implementation to the debugfs interface and the user space tool for
the user space users.

Note that the implementation supports only the user memory, as same to the idle
page access tracking feature.

[1] https://lore.kernel.org/linux-mm/20200706115322.29598-1-sjpark@amazon.com/ (local)

I am still struggling to find the benefit of this feature the way it
is implemented i.e. region based physical address space monitoring.
What exactly am I supposed to do for a given hot (or cold) physical
region? In a containerized world, that region can contain pages from
any cgroup. I can not really do anything about the accesses PHY-DAMON
provides me for a region.

Now if you give me per-page information that would be useful as I can
at least get per-cgroup accesses (idle or re-use data) but that would
be as costly as Page Idle Tracking.