Re: [PATCH v3 6/7] mm: list_lru: introduce folio_memcg_list_lru_alloc()

[Shakeel Butt]

On Wed, Mar 18, 2026 at 03:53:24PM -0400, Johannes Weiner wrote:
> memcg_list_lru_alloc() is called every time an object that may end up
> on the list_lru is created. It needs to quickly check if the list_lru
> heads for the memcg already exist, and allocate them when they don't.
> 
> Doing this with folio objects is tricky: folio_memcg() is not stable
> and requires either RCU protection or pinning the cgroup. But it's
> desirable to make the existence check lightweight under RCU, and only
> pin the memcg when we need to allocate list_lru heads and may block.
> 
> In preparation for switching the THP shrinker to list_lru, add a
> helper function for allocating list_lru heads coming from a folio.
> 
> Reviewed-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>