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

[Andrew Morton]

On Tue, 11 Aug 2026 13:31:55 -0700 Shakeel Butt <shakeel.butt@xxxxxxxxx> 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.
> 
> 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.

Thanks, I'll pluck this one as a hotfix.

It's old code, yes?  Are there any theories about why the sysbot issue
has just popped up?  Should we backport the fix?