Re: [RFC PATCH 2/2] mm/vmscan.c: Prevent allocating shrinker_info on offlined nodes

[Michal Hocko]

On Mon 06-12-21 16:19:12, Kirill Tkhai wrote:
> On 06.12.2021 13:45, David Hildenbrand wrote:
> >> This doesn't seen complete. Slab shrinkers are used in the reclaim
> >> context. Previously offline nodes could be onlined later and this would
> >> lead to NULL ptr because there is no hook to allocate new shrinker
> >> infos. This would be also really impractical because this would have to
> >> update all existing memcgs...
> > 
> > Instead of going through the trouble of updating...
> > 
> > ...  maybe just keep for_each_node() and check if the target node is
> > offline. If it's offline, just allocate from the first online node.
> > After all, we're not using __GFP_THISNODE, so there are no guarantees
> > either way ...
> 
> Hm, can't we add shrinker maps allocation to __try_online_node() in addition
> to this patch? 

Either that or through hotplug notifier (which would be a better
solution). But allocating a new shrinker map for each memcg would have
to be done as has been mentioned earlier.

-- 
Michal Hocko
SUSE Labs