Re: [PATCH v2 4/4] mm: thp: reparent the split queue during memcg offline

[David Hildenbrand]

On 25.09.25 08:11, Qi Zheng wrote:
> Hi David,

Hi :)

[...]

> > > +++ b/include/linux/mmzone.h
> > > @@ -1346,6 +1346,7 @@ struct deferred_split {
> > >        spinlock_t split_queue_lock;
> > >        struct list_head split_queue;
> > >        unsigned long split_queue_len;
> > > +    bool is_dying;
> >
> > It's a bit weird to query whether the "struct deferred_split" is dying.
> > Shouldn't this be a memcg property? (and in particular, not exist for
>
> There is indeed a CSS_DYING flag. But we must modify 'is_dying' under
> the protection of the split_queue_lock, otherwise the folio may be added
> back to the deferred_split of child memcg.

Is there no way to reuse the existing mechanisms, and find a way to have 
the shrinker / queue locking sync against that?

There is also the offline_css() function where we clear CSS_ONLINE. But 
it happens after calling ss->css_offline(css);

Being able to query "is the memcg going offline" and having a way to 
sync against that would be probably cleanest.

I'll let all the memcg people comment on how that could be done best.

> > the pglist_data part where it might not make sense at all?).
>
> Maybe:
>
> #ifdef CONFIG_MEMCG
>       bool is_dying;
> #endif

Still doesn't quite look like it would belong here :(

Also, is "dying" really the right terminology? It's more like "going 
offline"?

But then, the queue is not going offline, the memcg is ...

--
Cheers

David / dhildenb