Re: [RFC PATCH 0/3] mm, memcg: isolate deprecated v1 state from struct mem_cgroup

[Michal Hocko]

On Mon 02-11-26 14:15:52, Johannes Weiner wrote:
> On Mon, Nov 02, 2026 at 04:52:44PM +0000, Roman Gushchin wrote:
> > Tao Cui <cui.tao@xxxxxxxxx> writes:
> > 
> > > Hi Roman,
> > >
> > > 在 2026/10/30 14:05, Roman Gushchin 写道:
> > >> I believe we want to delete this code sooner than later, why would we rewrite it before that?
> > >> 
> > >
> > > My assumption was that v1 would still be maintained for some time
> > > before its eventual removal, and the goal was to reduce the coupling
> > > between the remaining v1 code and the shared core structures during
> > > that period, rather than to rewrite the implementation for its own
> > > sake.
> > 
> > I understand. But personally I don't see big issues with the current
> > code caused by the v1 stuff. Maybe I miss something...
> > 
> > The proposed changes on the other hand create difficulties for those
> > who use v1 and maintain some local changes or simple backport upstream
> > fixes. Of course, it's not a reason to not change the upstream code if
> > it's justified, but in this case I'm hardly convinced.
> > 
> > > If the expectation is that the remaining v1 implementation will be
> > > removed in the near future, then I agree this work becomes much harder
> > > to justify.
> > >
> > > Am I being too optimistic about how long the remaining v1 code is
> > > expected to stay around?
> > 
> > Well, Idk, it was considered deprecated for quite some time already,
> > so maybe announcing that it will be deleted in a year is reasonable?
> 
> That might be tougher for v1 users than the member placement :-)
> 
> My understanding is that there are still a few heavy v1 users out
> there. I'm not sure they can move within that timeframe. Personally I
> think the cost of the v1 code now is kind of negligible now?

Fully agreed. 
-- 
Michal Hocko
SUSE Labs