Re: [PATCH v2 2/2] mm: multi-gen LRU: fix NULL lruvec->pgdat deref in get_lruvec()

[Siddharth Chintamaneni]

On Mon, 19 Oct 2026 at 18:20, Barry Song <baohua@xxxxxxxxxx> wrote:
>
> On Tue, Oct 20, 2026 at 9:02 AM Siddharth Chintamaneni
> <sidchintamaneni@xxxxxxxxx> wrote:
> >
> [...]
> > >
> > > Thanks!
> > > I guess you mean the following:
> > >
> > > -module_init(kswapd_init)
> > > +//module_init(kswapd_init)
> > >
> > > Yes, I can reproduce it with the above as well.
> > >
> > > But kswapd_init() is definitely called before we enter userspace,
> > > so this doesn't seem to be an issue here?
> > >
> >
> > Looking at the callee sites of get_lruvec, all of them happen after
> > boot. So it should be fine. Anyway code clean up will address the
> > issue.
> >
> > > So I feel there is no bug here, but this cleanup is still welcome.
> >
> > Are you ok with the patch as is, or would you recommend  changing the
> > callsite of get_lruvec to mem_cgroup_lruvec?
>
> Overall, I'd be happy to see MGLRU-specific code being removed.
>
> If possible, could we split this into a two-patch series? The
> first patch would be this one, and the second would drop
> get_lruvec().
>
> In any case, if this isn't a bug fix, there's no need for a Fixes tag or
> a stable backport.
>

If that is the case, do we still need this patch?

> BTW, I've been struggling to understand why MGLRU introduced
> its own version in the first place. Maybe your follow-up
> patchset will help clarify that :-)
>

I have a theory -
when MGLRU was introduced lru_vec also returns NULL
https://elixir.bootlin.com/linux/v6.1.190/source/mm/vmscan.c#L3163
that is not the case anymore. I haven't looked at the refactoring that
happened later around it yet.
That might be the reason but I could be wrong.

> Best Regards
> Barry