Re: [PATCH] mm: vmpressure: don't count userspace-induced reclaim as memory pressure

[Michal Hocko]

On Thu 23-06-22 09:22:35, Yosry Ahmed wrote:
> On Thu, Jun 23, 2022 at 2:43 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
> >
> > On Thu 23-06-22 01:35:59, Yosry Ahmed wrote:
[...]
> > > In our internal version of memory.reclaim that we recently upstreamed,
> > > we do not account vmpressure during proactive reclaim (similar to how
> > > psi is handled upstream). We want to make sure this behavior also
> > > exists in the upstream version so that consolidating them does not
> > > break our users who rely on vmpressure and will start seeing increased
> > > pressure due to proactive reclaim.
> >
> > These are good reasons to have this patch in your tree. But why is this
> > patch benefitial for the upstream kernel? It clearly adds some code and
> > some special casing which will add a maintenance overhead.
> 
> It is not just Google, any existing vmpressure users will start seeing
> false pressure notifications with memory.reclaim. The main goal of the
> patch is to make sure memory.reclaim does not break pre-existing users
> of vmpressure, and doing it in a way that is consistent with psi makes
> sense.

memory.reclaim is v2 only feature which doesn't have vmpressure
interface. So I do not see how pre-existing users of the upstream kernel
can see any breakage.

-- 
Michal Hocko
SUSE Labs