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    SubjectRe: interaction of MADV_PAGEOUT with CoW anonymous mappings?
    On Wed, Mar 11, 2020 at 04:53:17PM -0700, Shakeel Butt wrote:
    > On Wed, Mar 11, 2020 at 1:45 AM Michal Hocko <mhocko@kernel.org> wrote:
    > >
    > > On Tue 10-03-20 15:48:31, Dave Hansen wrote:
    > > > Maybe instead of just punting on MADV_PAGEOUT for map_count>1 we should
    > > > only let it affect the *local* process. We could still put the page in
    > > > the swap cache, we just wouldn't go do the rmap walk.
    > >
    > > Is it really worth medling with the reclaim code and special case
    > > MADV_PAGEOUT there? I mean it is quite reasonable to have an initial
    > > implementation that doesn't really touch shared pages because that can
    > > lead to all sorts of hard to debug and unexpected problems. So I would
    > > much rather go with a simple patch to check map count first and see
    > > whether somebody actually cares about those shared pages and go from
    > > there.
    > >
    > > Minchan, do you want to take my diff and turn it into the proper patch
    > > or should I do it.
    > >
    >
    > What about the remote_madvise(MADV_PAGEOUT)? Will your patch disable
    > the pageout from that code path as well for pages with mapcount > 1?

    Maybe, not because process_madvise syscall needs more previliedge(ie,
    PTRACE_MODE_ATTACH_FSCREDS) so I guess it would be more secure.
    So in that case, I want to rely on the LRU chance for shared pages.

    With that, the manager process could give a hint to several processes
    and finally makes them paging out.

    What do you think?

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