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1/*
2 * Copyright (c) 2013 Red Hat, Inc. and Parallels Inc. All rights reserved.
3 * Authors: David Chinner and Glauber Costa
4 *
5 * Generic LRU infrastructure
6 */
7#ifndef _LRU_LIST_H
8#define _LRU_LIST_H
9
10#include <linux/list.h>
11#include <linux/nodemask.h>
12
13/* list_lru_walk_cb has to always return one of those */
14enum lru_status {
15 LRU_REMOVED, /* item removed from list */
16 LRU_ROTATE, /* item referenced, give another pass */
17 LRU_SKIP, /* item cannot be locked, skip */
18 LRU_RETRY, /* item not freeable. May drop the lock
19 internally, but has to return locked. */
20};
21
22struct list_lru_node {
23 spinlock_t lock;
24 struct list_head list;
25 /* kept as signed so we can catch imbalance bugs */
26 long nr_items;
27} ____cacheline_aligned_in_smp;
28
29struct list_lru {
30 struct list_lru_node *node;
31 nodemask_t active_nodes;
32};
33
34void list_lru_destroy(struct list_lru *lru);
35int list_lru_init(struct list_lru *lru);
36
37/**
38 * list_lru_add: add an element to the lru list's tail
39 * @list_lru: the lru pointer
40 * @item: the item to be added.
41 *
42 * If the element is already part of a list, this function returns doing
43 * nothing. Therefore the caller does not need to keep state about whether or
44 * not the element already belongs in the list and is allowed to lazy update
45 * it. Note however that this is valid for *a* list, not *this* list. If
46 * the caller organize itself in a way that elements can be in more than
47 * one type of list, it is up to the caller to fully remove the item from
48 * the previous list (with list_lru_del() for instance) before moving it
49 * to @list_lru
50 *
51 * Return value: true if the list was updated, false otherwise
52 */
53bool list_lru_add(struct list_lru *lru, struct list_head *item);
54
55/**
56 * list_lru_del: delete an element to the lru list
57 * @list_lru: the lru pointer
58 * @item: the item to be deleted.
59 *
60 * This function works analogously as list_lru_add in terms of list
61 * manipulation. The comments about an element already pertaining to
62 * a list are also valid for list_lru_del.
63 *
64 * Return value: true if the list was updated, false otherwise
65 */
66bool list_lru_del(struct list_lru *lru, struct list_head *item);
67
68/**
69 * list_lru_count_node: return the number of objects currently held by @lru
70 * @lru: the lru pointer.
71 * @nid: the node id to count from.
72 *
73 * Always return a non-negative number, 0 for empty lists. There is no
74 * guarantee that the list is not updated while the count is being computed.
75 * Callers that want such a guarantee need to provide an outer lock.
76 */
77unsigned long list_lru_count_node(struct list_lru *lru, int nid);
78static inline unsigned long list_lru_count(struct list_lru *lru)
79{
80 long count = 0;
81 int nid;
82
83 for_each_node_mask(nid, lru->active_nodes)
84 count += list_lru_count_node(lru, nid);
85
86 return count;
87}
88
89typedef enum lru_status
90(*list_lru_walk_cb)(struct list_head *item, spinlock_t *lock, void *cb_arg);
91/**
92 * list_lru_walk_node: walk a list_lru, isolating and disposing freeable items.
93 * @lru: the lru pointer.
94 * @nid: the node id to scan from.
95 * @isolate: callback function that is resposible for deciding what to do with
96 * the item currently being scanned
97 * @cb_arg: opaque type that will be passed to @isolate
98 * @nr_to_walk: how many items to scan.
99 *
100 * This function will scan all elements in a particular list_lru, calling the
101 * @isolate callback for each of those items, along with the current list
102 * spinlock and a caller-provided opaque. The @isolate callback can choose to
103 * drop the lock internally, but *must* return with the lock held. The callback
104 * will return an enum lru_status telling the list_lru infrastructure what to
105 * do with the object being scanned.
106 *
107 * Please note that nr_to_walk does not mean how many objects will be freed,
108 * just how many objects will be scanned.
109 *
110 * Return value: the number of objects effectively removed from the LRU.
111 */
112unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
113 list_lru_walk_cb isolate, void *cb_arg,
114 unsigned long *nr_to_walk);
115
116static inline unsigned long
117list_lru_walk(struct list_lru *lru, list_lru_walk_cb isolate,
118 void *cb_arg, unsigned long nr_to_walk)
119{
120 long isolated = 0;
121 int nid;
122
123 for_each_node_mask(nid, lru->active_nodes) {
124 isolated += list_lru_walk_node(lru, nid, isolate,
125 cb_arg, &nr_to_walk);
126 if (nr_to_walk <= 0)
127 break;
128 }
129 return isolated;
130}
131#endif /* _LRU_LIST_H */