Re: [PATCH RFC v2 0/4] mm/ksm: add option to automerge VMAs

From: Michal Hocko
Date: Wed May 15 2019 - 10:53:45 EST

[Cc Suren and Minchan - the email thread starts here 20190514131654.25463-1-oleksandr@xxxxxxxxxx]

On Wed 15-05-19 08:53:11, Michal Hocko wrote:
> I will try to comment on the interface itself later. But I have to say
> that I am not impressed. Abusing sysfs for per process features is quite
> gross to be honest.

I have already commented on this in other email. I consider sysfs an
unsuitable interface for per-process API. Not to mention this particular
one is very KSM specific while the question about setting different
hints on memory of a remote process is a more generic question. As
already mentioned there are usecases where people would like to say
that a certain memory is cold from outside of the process context (e.g.
monitor application). So essentially a form of a user space memory
management. And this usecase sounds a bit similar to me and having a
common api sounds more sensible to me.

One thing we were discussing at LSFMM this year was a way to either
provide madvise_remote(pid, addr, length, advice) or a fadvise
alternative over /proc/<pid>/map_vmas/<range> file descriptors
(essentially resembling the existing map_files api) to achieve such a
functionality. This is still a very rough idea but the api would sound
much more generic to me and it would allow much wider range of usecases.

But maybe I am completely wrong and this is just opens a can of worms
that we do not want.
Michal Hocko