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

[Yosry Ahmed]

On Tue, Oct 17, 2023 at 4:21 PM Nhat Pham <nphamcs@xxxxxxxxx> 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@xxxxxxxxx>

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.

> ---
>  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