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/*
* 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>
/* list_lru_walk_cb has to always return one of those */
enum lru_status {
LRU_REMOVED, /* item removed from list */
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 {
spinlock_t lock;
struct list_head list;
/* kept as signed so we can catch imbalance bugs */
long nr_items;
};
int list_lru_init(struct list_lru *lru);
/**
* 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: return the number of objects currently held by @lru
* @lru: the lru pointer.
*
* 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.
*/
static inline unsigned long list_lru_count(struct list_lru *lru)
{
return lru->nr_items;
}
typedef enum lru_status
(*list_lru_walk_cb)(struct list_head *item, spinlock_t *lock, void *cb_arg);
/**
* list_lru_walk: walk a list_lru, isolating and disposing freeable items.
* @lru: the lru pointer.
* @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(struct list_lru *lru, list_lru_walk_cb isolate,
void *cb_arg, unsigned long nr_to_walk);
typedef void (*list_lru_dispose_cb)(struct list_head *dispose_list);
/**
* list_lru_dispose_all: forceably flush all elements in an @lru
* @lru: the lru pointer
* @dispose: callback function to be called for each lru list.
*
* This function will forceably isolate all elements into the dispose list, and
* call the @dispose callback to flush the list. Please note that the callback
* should expect items in any state, clean or dirty, and be able to flush all of
* them.
*
* Return value: how many objects were freed. It should be equal to all objects
* in the list_lru.
*/
unsigned long
list_lru_dispose_all(struct list_lru *lru, list_lru_dispose_cb dispose);
#endif /* _LRU_LIST_H */
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