Re: [PATCH] memcg: force charge kmem counter too

Minchan Kim
2018-05-31T06:01:33Z

On Wed, May 30, 2018 at 11:14:33AM -0700, Shakeel Butt wrote:
> On Tue, May 29, 2018 at 1:31 AM, Michal Hocko <mhocko@kernel.org> wrote:
> > On Mon 28-05-18 10:23:07, Shakeel Butt wrote:
> >> On Mon, May 28, 2018 at 2:11 AM, Michal Hocko <mhocko@kernel.org> wrote:
> >> Though is there a precedence where the broken feature is not fixed
> >> because an alternative is available?
> >
> > Well, I can see how breaking GFP_NOFAIL semantic is problematic, on the
> > other hand we keep saying that kmem accounting in v1 is hard usable and
> > strongly discourage people from using it. Sure we can add the code which
> > handles _this_ particular case but that wouldn't make the whole thing
> > more usable I strongly suspect. Maybe I am wrong and you can provide
> > some specific examples. Is GFP_NOFAIL that common to matter?
> >
> > In any case we should balance between the code maintainability here.
> > Adding more cruft into the allocator path is not free.
> >
>
> We do not use kmem limits internally and this is something I found
> through code inspection. If this patch is increasing the cost of code
> maintainability I am fine with dropping it but at least there should a
> comment saying that kmem limits are broken and no need fix.

I agree.

Even, I didn't know kmem is strongly discouraged until now. Then,
why is it enabled by default on cgroup v1?

Let's turn if off with comment "It's broken so do not use/fix. Instead,
please move to cgroup v2".