Re: [PATCH 3/3] mm/mincore: provide mapped status when cached status is not allowed

From: Jiri Kosina
Date: Wed Feb 06 2019 - 15:14:35 EST

On Fri, 1 Feb 2019, Vlastimil Babka wrote:

> > Well, but rss update will not tell you that the page has been faulted in
> > which is the most interesting part.
> Sure, but the patch doesn't add back that capability neither. It allows
> to recognize page being reclaimed, and I argue you can infer that from
> rss change as well. That change is mentioned in the last paragraph in
> changelog, and I thought "add a hard to evaluate side channel" in your
> reply referred to that. It doesn't add back the "original" side channel
> to detect somebody else accessed a page.

On Fri, 1 Feb 2019, Vlastimil Babka wrote:

> > Is this really worth it? Do we know about any specific usecase that
> > would benefit from this change? TBH I would rather wait for the report
> > than add a hard to evaluate side channel.
> Well it's not that complicated IMHO. Linus said it's worth trying, so
> let's see how he likes the result. The side channel exists anyway as
> long as process can e.g. check if its rss shrinked, and I doubt we are
> going to remove that possibility.

Linus, do you have any opinion here?

I have a hunch that mm maintainers are keeping this on a backburner
because there might still open question(s) in the air.


Jiri Kosina