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    SubjectRe: [PATCH v5 1/6] mm/page_idle: Add per-pid idle page tracking using virtual index
    On Tue, Aug 13, 2019 at 04:14:32PM +0200, Michal Hocko wrote:
    [snip]
    > > > If the API is flawed then this is likely going
    > > > to kick us later and will be hard to fix. I am still not convinced about
    > > > the swap part of the thing TBH.
    > >
    > > Ok, then let us discuss it. As I mentioned before, without this we lose the
    > > access information due to MADVISE or swapping. Minchan and Konstantin both
    > > suggested it that's why I also added it (other than me also realizing that it
    > > is neeed).
    >
    > I have described my concerns about the general idle bit behavior after
    > unmapping pointing to discrepancy with !anon pages. And I believe those
    > haven't been addressed yet.

    You are referring to this post right?
    https://lkml.org/lkml/2019/8/6/637

    Specifically your question was:
    How are you going to handle situation when the page is unmapped and refaulted again (e.g. a normal reclaim of a pagecache)?

    Currently I don't know how to implement that. Would it work if I stored the
    page-idle bit information in the pte of the file page (after the page is
    unmapped by reclaim?).

    Also, this could be a future extension - the Android heap profiler does not
    need it right now. I know that's not a good argument but it is useful to say
    that it doesn't affect a real world usecase.. the swap issue on the other
    hand, is a real usecase. Since the profiler should not get affected by
    swapping or MADVISE_COLD hints.

    > Besides that I am still not seeing any
    > description of the usecase that would suffer from the lack of the
    > functionality in changelogs.

    You are talking about the swap usecase? The usecase is well layed out in v5
    2/6. Did you see it? https://lore.kernel.org/patchwork/patch/1112283/

    thanks,

    - Joel

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