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

[Johannes Weiner <hannes@cmpxchg.org>]

On Tue, Mar 24, 2026 at 12:01:55PM +0000, Lorenzo Stoakes (Oracle) wrote:
> 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@kernel.org>
> > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> 
> Logic LGTM, but would be nice to have some kdoc. With that addressed, feel free
> to add:
> 
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Thanks!

> >  include/linux/list_lru.h | 12 ++++++++++++
> >  mm/list_lru.c            | 39 ++++++++++++++++++++++++++++++++++-----
> >  2 files changed, 46 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
> > index 4afc02deb44d..4bd29b61c59a 100644
> > --- a/include/linux/list_lru.h
> > +++ b/include/linux/list_lru.h
> > @@ -81,6 +81,18 @@ static inline int list_lru_init_memcg_key(struct list_lru *lru, struct shrinker
> >
> >  int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
> >  			 gfp_t gfp);
> > +
> > +#ifdef CONFIG_MEMCG
> > +int folio_memcg_list_lru_alloc(struct folio *folio, struct list_lru *lru,
> > +			       gfp_t gfp);
> 
> Could we have a kdoc comment for this? Thanks!

And one kdoc comment.

Your total will be 8.75, you can pull up to the next window, sir.