linux-kernel - Re: [PATCH] mm/memcontrol: respect zswap.writeback setting from parent cg too

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Message-ID: <CAKEwX=Pz4Pe-CAevBvxUCpPZJ-fRseLN4T35Wt3mb84gqCY25w@mail.gmail.com>
Date: Thu, 15 Aug 2024 16:31:50 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Mike Yuan <me@...dnzj.com>, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, cgroups@...r.kernel.org, 
	Muchun Song <muchun.song@...ux.dev>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Michal Hocko <mhocko@...nel.org>, 
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] mm/memcontrol: respect zswap.writeback setting from
 parent cg too

On Thu, Aug 15, 2024 at 3:10 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> On Thu, Aug 15, 2024 at 3:08 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > On Thu, 15 Aug 2024 12:12:26 -0700 Nhat Pham <nphamcs@...il.com> wrote:
> >
> > > > Yeah, I thought about the other way around and reached the same
> > > > conclusion.
> > > > And there's permission boundary in the mix too - if root disables zswap
> > > > writeback for its cgroup, the subcgroups, which could possibly be owned
> > > > by other users, should not be able to reenable this.
> > >
> > > Hmm yeah, I think I agree with your and Yosry's reasonings :) It
> > > doesn't affect our use case AFAICS, and the code looks solid to me,
> > > so:
> > >
> > > Reviewed-by: Nhat Pham <nphamcs@...il.com>
> >
> > But you'd still like an update to Documentation/admin-guide/cgroup-v2.rst?
>
>
> Yeah I'd rather see a v2 with updated docs, and hopefully a selftest
> if the existing tests problem is resolved.

Ah yeah, I was thinking this could be done in a follow-up patch.

But yes, please - documentation. Preferably everything together as v2.

>
> Also, do we want a Fixes tag and to backport this so that current
> users get the new behavior ASAP?

Hmm, I wonder if it's more confusing for users to change the behavior
in older kernels.

(OTOH, if this already is what people expect, then yeah it's a good
idea to backport).