Re: [PATCH v3 1/5] mm: list_lru: allow external numa node and cgroup tracking

[Nhat Pham <nphamcs@gmail.com>]

On Wed, Oct 18, 2023 at 3:27 PM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> On Tue, Oct 17, 2023 at 4:21 PM Nhat Pham <nphamcs@gmail.com> wrote:
> >
> > The interface of list_lru is based on the assumption that objects are
> > allocated on the correct node/memcg, with this change it is introduced the
> > possibility to explicitly specify numa node and memcgroup when adding and
> > removing objects. This is so that users of list_lru can track node/memcg
> > of the items outside of the list_lru, like in zswap, where the allocations
> > can be made by kswapd for data that's charged to a different cgroup.
> >
> > Signed-off-by: Nhat Pham <nphamcs@gmail.com>
>
> I prefer what Johannes suggested, making list_lru_add() and friends
> take in the memcg and nid, and add list_lru_add_obj() (or similar) and
> friends that assume the object is on the right node and memcg. This is
> clearer and more explicit imo. I am not very familiar with list_lrus
> though, so I'll leave this to folks who actually are.

Yeah the original naming is... most unfortunate, to say the least :)

I create a new function to avoid renaming list_lru_add's usage
everywhere, but if the consensus is that everyone prefers
list_lru_add() to be the one taking memcg + nid (and the original
renamed to list_lru_add_obj()), I can go around fixing all of it :)

Seems like a separate endeavour though.

>
> > ---
> >  include/linux/list_lru.h | 38 +++++++++++++++++++++++++++++++++++
> >  mm/list_lru.c            | 43 +++++++++++++++++++++++++++++++++++-----
> >  2 files changed, 76 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
> > index b35968ee9fb5..0f5f39cacbbb 100644
> > --- a/include/linux/list_lru.h
> > +++ b/include/linux/list_lru.h
> > @@ -89,6 +89,24 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren
> >   */
> >  bool list_lru_add(struct list_lru *lru, struct list_head *item);
> >
> > +/**
> > + * __list_lru_add: add an element to a specific sublist.
> > + * @list_lru: the lru pointer
> > + * @item: the item to be added.
> > + * @memcg: the cgroup of the sublist to add the item to.
> > + * @nid: the node id of the sublist to add the item to.
> > + *
> > + * This function is similar to list_lru_add(), but it allows the caller to
> > + * specify the sublist to which the item should be added. This can be useful
> > + * when the list_head node is not necessarily in the same cgroup and NUMA node
> > + * as the data it represents, such as zswap, where the list_head node could be
> > + * from kswapd and the data from a different cgroup altogether.
> > + *
> > + * Return value: true if the list was updated, false otherwise
> > + */
> > +bool __list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
> > +                   struct mem_cgroup *memcg);
> > +
> >  /**
> >   * list_lru_del: delete an element to the lru list
> >   * @list_lru: the lru pointer
> > @@ -102,6 +120,18 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item);
> >   */
> >  bool list_lru_del(struct list_lru *lru, struct list_head *item);
> >
> > +/**
> > + * __list_lru_del: delete an element from a specific sublist.
> > + * @list_lru: the lru pointer
> > + * @item: the item to be deleted.
> > + * @memcg: the cgroup of the sublist to delete the item from.
> > + * @nid: the node id of the sublist to delete the item from.
> > + *
> > + * Return value: true if the list was updated, false otherwise.
> > + */
> > +bool __list_lru_del(struct list_lru *lru, struct list_head *item, int nid,
> > +                   struct mem_cgroup *memcg);
> > +
> >  /**
> >   * list_lru_count_one: return the number of objects currently held by @lru
> >   * @lru: the lru pointer.
> > @@ -136,6 +166,14 @@ static inline unsigned long list_lru_count(struct list_lru *lru)
> >  void list_lru_isolate(struct list_lru_one *list, struct list_head *item);
> >  void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item,
> >                            struct list_head *head);
> > +/*
> > + * list_lru_putback: undo list_lru_isolate.
> > + *
> > + * Since we might have dropped the LRU lock in between, recompute list_lru_one
> > + * from the node's id and memcg.
> > + */
> > +void list_lru_putback(struct list_lru *lru, struct list_head *item, int nid,
> > +                     struct mem_cgroup *memcg);
> >
> >  typedef enum lru_status (*list_lru_walk_cb)(struct list_head *item,
> >                 struct list_lru_one *list, spinlock_t *lock, void *cb_arg);
> > diff --git a/mm/list_lru.c b/mm/list_lru.c
> > index a05e5bef3b40..63b75163c6ad 100644
> > --- a/mm/list_lru.c
> > +++ b/mm/list_lru.c
> > @@ -119,13 +119,22 @@ list_lru_from_kmem(struct list_lru *lru, int nid, void *ptr,
> >  bool list_lru_add(struct list_lru *lru, struct list_head *item)
> >  {
> >         int nid = page_to_nid(virt_to_page(item));
> > +       struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ?
> > +               mem_cgroup_from_slab_obj(item) : NULL;
> > +
> > +       return __list_lru_add(lru, item, nid, memcg);
> > +}
> > +EXPORT_SYMBOL_GPL(list_lru_add);
> > +
> > +bool __list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
> > +                   struct mem_cgroup *memcg)
> > +{
> >         struct list_lru_node *nlru = &lru->node[nid];
> > -       struct mem_cgroup *memcg;
> >         struct list_lru_one *l;
> >
> >         spin_lock(&nlru->lock);
> >         if (list_empty(item)) {
> > -               l = list_lru_from_kmem(lru, nid, item, &memcg);
> > +               l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
> >                 list_add_tail(item, &l->list);
> >                 /* Set shrinker bit if the first element was added */
> >                 if (!l->nr_items++)
> > @@ -138,17 +147,27 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item)
> >         spin_unlock(&nlru->lock);
> >         return false;
> >  }
> > -EXPORT_SYMBOL_GPL(list_lru_add);
> > +EXPORT_SYMBOL_GPL(__list_lru_add);
> >
> >  bool list_lru_del(struct list_lru *lru, struct list_head *item)
> >  {
> >         int nid = page_to_nid(virt_to_page(item));
> > +       struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ?
> > +               mem_cgroup_from_slab_obj(item) : NULL;
> > +
> > +       return __list_lru_del(lru, item, nid, memcg);
> > +}
> > +EXPORT_SYMBOL_GPL(list_lru_del);
> > +
> > +bool __list_lru_del(struct list_lru *lru, struct list_head *item, int nid,
> > +                   struct mem_cgroup *memcg)
> > +{
> >         struct list_lru_node *nlru = &lru->node[nid];
> >         struct list_lru_one *l;
> >
> >         spin_lock(&nlru->lock);
> >         if (!list_empty(item)) {
> > -               l = list_lru_from_kmem(lru, nid, item, NULL);
> > +               l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
> >                 list_del_init(item);
> >                 l->nr_items--;
> >                 nlru->nr_items--;
> > @@ -158,7 +177,7 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item)
> >         spin_unlock(&nlru->lock);
> >         return false;
> >  }
> > -EXPORT_SYMBOL_GPL(list_lru_del);
> > +EXPORT_SYMBOL_GPL(__list_lru_del);
> >
> >  void list_lru_isolate(struct list_lru_one *list, struct list_head *item)
> >  {
> > @@ -175,6 +194,20 @@ void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item,
> >  }
> >  EXPORT_SYMBOL_GPL(list_lru_isolate_move);
> >
> > +void list_lru_putback(struct list_lru *lru, struct list_head *item, int nid,
> > +                     struct mem_cgroup *memcg)
> > +{
> > +       struct list_lru_one *list =
> > +               list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
> > +
> > +       if (list_empty(item)) {
> > +               list_add_tail(item, &list->list);
> > +               if (!list->nr_items++)
> > +                       set_shrinker_bit(memcg, nid, lru_shrinker_id(lru));
> > +       }
> > +}
> > +EXPORT_SYMBOL_GPL(list_lru_putback);
> > +
> >  unsigned long list_lru_count_one(struct list_lru *lru,
> >                                  int nid, struct mem_cgroup *memcg)
> >  {
> > --
> > 2.34.1