Re: [PATCH 1/9] memcg: make the v1 soft limit knob inert

[Shakeel Butt]

On Thu, Aug 13, 2026 at 10:22:57AM +0200, Michal Hocko wrote:
> On Tue 11-08-26 13:31:55, Shakeel Butt wrote:
> > The v1 soft limit has been deprecated since v6.12 and nobody has
> > reported depending on it. Start the removal by decoupling the interface
> > from the implementation: keep memory.soft_limit_in_bytes, but ignore
> > writes to it and always report the maximum value on read similar to
> > what memory.kmem.limit_in_bytes already does.
> > 
> > Writes are still parsed, so malformed input keeps returning -EINVAL.
> > The knob now also behaves the same everywhere: it used to return
> > -EOPNOTSUPP on PREEMPT_RT, where soft limit reclaim has always been
> > disabled.
> 
> Is there any specific reason to not return EOPNOTSUPP for everybody now?

I followed the memory.kmem.limit_in_bytes example. If you have strong opinion, I
am ok with EOPNOTSUPP as well.

> 
> > This also fixes the syzbot report linked below. Soft limit reclaim is
> > the only caller that runs shrink_lruvec() from kswapd against a
> > specific memcg, so it is the only way to reach lru_gen_shrink_lruvec()
> > and in turn set_mm_walk(), which warns when called from kswapd.
> > 
> > Reported-by: syzbot+12ee2725d5fde63a9c96@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Closes: https://lore.kernel.org/all/6a7a6929.b50370da.49fe0.005e.GAE@xxxxxxxxxx/
> > Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> 
> Anyway
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>

Thanks for reviewing the series.