Re: [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] 

quoted

quoted

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