On Wed, Mar 18, 2015 at 11:44:33PM +0300, Vladimir Davydov wrote:

Usage:

 1. Write 1 to /proc/sys/vm/set_idle.

    This will set the IDLE flag for all user pages. The IDLE flag is cleared
    when the page is read or the ACCESS/YOUNG bit is cleared in any PTE pointing
    to the page. It is also cleared when the page is freed.

 2. Wait some time.

 3. Write 6 to /proc/PID/clear_refs for each PID of interest.

    This will clear the IDLE flag for recently accessed pages.

 4. Count the number of idle pages as reported by /proc/kpageflags. One may use
    /proc/PID/pagemap and/or /proc/kpagecgroup to filter pages that belong to a
    certain application/container.

Any more thoughts on this? I am particularly interested in the user
interface. I think that /proc/kpagecgroup is OK, but I have my
reservations about using /proc/sys/vm/set_idle and /proc/PID/clear_refs
for setting and clearing the idle flag. The point is it is impossible to
scan memory for setting/clearing page idle flags in the background with
some predefined rate - one has to scan it all at once, which might
result in CPU load spikes on huge machines with TBs of RAM. May be, we'd
better introduce /proc/sys/vm/{set_idle,clear_refs_idle}, which would
receive pfn range to set/clear idle flags?

Any thoughts/ideas are more than welcome.

Thanks,
Vladimir