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    SubjectRe: [RFC v7 00/10] DAMON: Support Physical Memory Address Space Monitoring
    On Tue, Aug 18, 2020 at 12:25 AM SeongJae Park <sjpark@amazon.com> wrote:
    >
    > From: SeongJae Park <sjpark@amazon.de>
    >
    > 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/
    >

    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.

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