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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 | ||
12 | /* list_lru_walk_cb has to always return one of those */ | |
13 | enum lru_status { | |
14 | LRU_REMOVED, /* item removed from list */ | |
15 | LRU_ROTATE, /* item referenced, give another pass */ | |
16 | LRU_SKIP, /* item cannot be locked, skip */ | |
17 | LRU_RETRY, /* item not freeable. May drop the lock | |
18 | internally, but has to return locked. */ | |
19 | }; | |
20 | ||
21 | struct list_lru { | |
22 | spinlock_t lock; | |
23 | struct list_head list; | |
24 | /* kept as signed so we can catch imbalance bugs */ | |
25 | long nr_items; | |
26 | }; | |
27 | ||
28 | int list_lru_init(struct list_lru *lru); | |
29 | ||
30 | /** | |
31 | * list_lru_add: add an element to the lru list's tail | |
32 | * @list_lru: the lru pointer | |
33 | * @item: the item to be added. | |
34 | * | |
35 | * If the element is already part of a list, this function returns doing | |
36 | * nothing. Therefore the caller does not need to keep state about whether or | |
37 | * not the element already belongs in the list and is allowed to lazy update | |
38 | * it. Note however that this is valid for *a* list, not *this* list. If | |
39 | * the caller organize itself in a way that elements can be in more than | |
40 | * one type of list, it is up to the caller to fully remove the item from | |
41 | * the previous list (with list_lru_del() for instance) before moving it | |
42 | * to @list_lru | |
43 | * | |
44 | * Return value: true if the list was updated, false otherwise | |
45 | */ | |
46 | bool list_lru_add(struct list_lru *lru, struct list_head *item); | |
47 | ||
48 | /** | |
49 | * list_lru_del: delete an element to the lru list | |
50 | * @list_lru: the lru pointer | |
51 | * @item: the item to be deleted. | |
52 | * | |
53 | * This function works analogously as list_lru_add in terms of list | |
54 | * manipulation. The comments about an element already pertaining to | |
55 | * a list are also valid for list_lru_del. | |
56 | * | |
57 | * Return value: true if the list was updated, false otherwise | |
58 | */ | |
59 | bool list_lru_del(struct list_lru *lru, struct list_head *item); | |
60 | ||
61 | /** | |
62 | * list_lru_count: return the number of objects currently held by @lru | |
63 | * @lru: the lru pointer. | |
64 | * | |
65 | * Always return a non-negative number, 0 for empty lists. There is no | |
66 | * guarantee that the list is not updated while the count is being computed. | |
67 | * Callers that want such a guarantee need to provide an outer lock. | |
68 | */ | |
69 | static inline unsigned long list_lru_count(struct list_lru *lru) | |
70 | { | |
71 | return lru->nr_items; | |
72 | } | |
73 | ||
74 | typedef enum lru_status | |
75 | (*list_lru_walk_cb)(struct list_head *item, spinlock_t *lock, void *cb_arg); | |
76 | /** | |
77 | * list_lru_walk: walk a list_lru, isolating and disposing freeable items. | |
78 | * @lru: the lru pointer. | |
79 | * @isolate: callback function that is resposible for deciding what to do with | |
80 | * the item currently being scanned | |
81 | * @cb_arg: opaque type that will be passed to @isolate | |
82 | * @nr_to_walk: how many items to scan. | |
83 | * | |
84 | * This function will scan all elements in a particular list_lru, calling the | |
85 | * @isolate callback for each of those items, along with the current list | |
86 | * spinlock and a caller-provided opaque. The @isolate callback can choose to | |
87 | * drop the lock internally, but *must* return with the lock held. The callback | |
88 | * will return an enum lru_status telling the list_lru infrastructure what to | |
89 | * do with the object being scanned. | |
90 | * | |
91 | * Please note that nr_to_walk does not mean how many objects will be freed, | |
92 | * just how many objects will be scanned. | |
93 | * | |
94 | * Return value: the number of objects effectively removed from the LRU. | |
95 | */ | |
96 | unsigned long list_lru_walk(struct list_lru *lru, list_lru_walk_cb isolate, | |
97 | void *cb_arg, unsigned long nr_to_walk); | |
98 | ||
99 | typedef void (*list_lru_dispose_cb)(struct list_head *dispose_list); | |
100 | /** | |
101 | * list_lru_dispose_all: forceably flush all elements in an @lru | |
102 | * @lru: the lru pointer | |
103 | * @dispose: callback function to be called for each lru list. | |
104 | * | |
105 | * This function will forceably isolate all elements into the dispose list, and | |
106 | * call the @dispose callback to flush the list. Please note that the callback | |
107 | * should expect items in any state, clean or dirty, and be able to flush all of | |
108 | * them. | |
109 | * | |
110 | * Return value: how many objects were freed. It should be equal to all objects | |
111 | * in the list_lru. | |
112 | */ | |
113 | unsigned long | |
114 | list_lru_dispose_all(struct list_lru *lru, list_lru_dispose_cb dispose); | |
115 | #endif /* _LRU_LIST_H */ |