include/linux/list_lru.h

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Copyright (c) 2013 Red Hat, Inc. and Parallels Inc. All rights reserved.
 * Authors: David Chinner and Glauber Costa
 *
 * Generic LRU infrastructure
 */
#ifndef _LRU_LIST_H
#define _LRU_LIST_H

#include <linux/list.h>
#include <linux/nodemask.h>
#include <linux/shrinker.h>

struct mem_cgroup;

/* list_lru_walk_cb has to always return one of those */
enum lru_status {
	LRU_REMOVED,		/* item removed from list */
	LRU_REMOVED_RETRY,	/* item removed, but lock has been
				   dropped and reacquired */
	LRU_ROTATE,		/* item referenced, give another pass */
	LRU_SKIP,		/* item cannot be locked, skip */
	LRU_RETRY,		/* item not freeable. May drop the lock
				   internally, but has to return locked. */
};

struct list_lru_one {
	struct list_head	list;
	/* may become negative during memcg reparenting */
	long			nr_items;
};

struct list_lru_memcg {
	struct rcu_head		rcu;
	/* array of per cgroup lists, indexed by memcg_cache_id */
	struct list_lru_one	*lru[0];
};

struct list_lru_node {
	/* protects all lists on the node, including per cgroup */
	spinlock_t		lock;
	/* global list, used for the root cgroup in cgroup aware lrus */
	struct list_lru_one	lru;
#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
	/* for cgroup aware lrus points to per cgroup lists, otherwise NULL */
	struct list_lru_memcg	__rcu *memcg_lrus;
#endif
	long nr_items;
} ____cacheline_aligned_in_smp;

struct list_lru {
	struct list_lru_node	*node;
#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
	struct list_head	list;
#endif
};

void list_lru_destroy(struct list_lru *lru);
int __list_lru_init(struct list_lru *lru, bool memcg_aware,
		    struct lock_class_key *key);

#define list_lru_init(lru)		__list_lru_init((lru), false, NULL)
#define list_lru_init_key(lru, key)	__list_lru_init((lru), false, (key))
#define list_lru_init_memcg(lru)	__list_lru_init((lru), true, NULL)

int memcg_update_all_list_lrus(int num_memcgs);
void memcg_drain_all_list_lrus(int src_idx, int dst_idx);

/**
 * list_lru_add: add an element to the lru list's tail
 * @list_lru: the lru pointer
 * @item: the item to be added.
 *
 * If the element is already part of a list, this function returns doing
 * nothing. Therefore the caller does not need to keep state about whether or
 * not the element already belongs in the list and is allowed to lazy update
 * it. Note however that this is valid for *a* list, not *this* list. If
 * the caller organize itself in a way that elements can be in more than
 * one type of list, it is up to the caller to fully remove the item from
 * the previous list (with list_lru_del() for instance) before moving it
 * to @list_lru
 *
 * Return value: true if the list was updated, false otherwise
 */
bool list_lru_add(struct list_lru *lru, struct list_head *item);

/**
 * list_lru_del: delete an element to the lru list
 * @list_lru: the lru pointer
 * @item: the item to be deleted.
 *
 * This function works analogously as list_lru_add in terms of list
 * manipulation. The comments about an element already pertaining to
 * a list are also valid for list_lru_del.
 *
 * Return value: true if the list was updated, false otherwise
 */
bool list_lru_del(struct list_lru *lru, struct list_head *item);

/**
 * list_lru_count_one: return the number of objects currently held by @lru
 * @lru: the lru pointer.
 * @nid: the node id to count from.
 * @memcg: the cgroup to count from.
 *
 * Always return a non-negative number, 0 for empty lists. There is no
 * guarantee that the list is not updated while the count is being computed.
 * Callers that want such a guarantee need to provide an outer lock.
 */
unsigned long list_lru_count_one(struct list_lru *lru,
				 int nid, struct mem_cgroup *memcg);
unsigned long list_lru_count_node(struct list_lru *lru, int nid);

static inline unsigned long list_lru_shrink_count(struct list_lru *lru,
						  struct shrink_control *sc)
{
	return list_lru_count_one(lru, sc->nid, sc->memcg);
}

static inline unsigned long list_lru_count(struct list_lru *lru)
{
	long count = 0;
	int nid;

	for_each_node_state(nid, N_NORMAL_MEMORY)
		count += list_lru_count_node(lru, nid);

	return count;
}

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);

typedef enum lru_status (*list_lru_walk_cb)(struct list_head *item,
		struct list_lru_one *list, spinlock_t *lock, void *cb_arg);

/**
 * list_lru_walk_one: walk a list_lru, isolating and disposing freeable items.
 * @lru: the lru pointer.
 * @nid: the node id to scan from.
 * @memcg: the cgroup to scan from.
 * @isolate: callback function that is resposible for deciding what to do with
 *  the item currently being scanned
 * @cb_arg: opaque type that will be passed to @isolate
 * @nr_to_walk: how many items to scan.
 *
 * This function will scan all elements in a particular list_lru, calling the
 * @isolate callback for each of those items, along with the current list
 * spinlock and a caller-provided opaque. The @isolate callback can choose to
 * drop the lock internally, but *must* return with the lock held. The callback
 * will return an enum lru_status telling the list_lru infrastructure what to
 * do with the object being scanned.
 *
 * Please note that nr_to_walk does not mean how many objects will be freed,
 * just how many objects will be scanned.
 *
 * Return value: the number of objects effectively removed from the LRU.
 */
unsigned long list_lru_walk_one(struct list_lru *lru,
				int nid, struct mem_cgroup *memcg,
				list_lru_walk_cb isolate, void *cb_arg,
				unsigned long *nr_to_walk);
unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
				 list_lru_walk_cb isolate, void *cb_arg,
				 unsigned long *nr_to_walk);

static inline unsigned long
list_lru_shrink_walk(struct list_lru *lru, struct shrink_control *sc,
		     list_lru_walk_cb isolate, void *cb_arg)
{
	return list_lru_walk_one(lru, sc->nid, sc->memcg, isolate, cb_arg,
				 &sc->nr_to_scan);
}

static inline unsigned long
list_lru_walk(struct list_lru *lru, list_lru_walk_cb isolate,
	      void *cb_arg, unsigned long nr_to_walk)
{
	long isolated = 0;
	int nid;

	for_each_node_state(nid, N_NORMAL_MEMORY) {
		isolated += list_lru_walk_node(lru, nid, isolate,
					       cb_arg, &nr_to_walk);
		if (nr_to_walk <= 0)
			break;
	}
	return isolated;
}
#endif /* _LRU_LIST_H */