list: add a new LRU list type

/*

 * 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 */

			   util.o mmzone.o vmstat.o backing-dev.o \

			   mm_init.o mmu_context.o percpu.o slab_common.o \

			   compaction.o balloon_compaction.o \

			   interval_tree.o $(mmu-y)

			   interval_tree.o list_lru.o $(mmu-y)

obj-y += init-mm.o

/*

 * Copyright (c) 2013 Red Hat, Inc. and Parallels Inc. All rights reserved.

 * Authors: David Chinner and Glauber Costa

 *

 * Generic LRU infrastructure

 */

#include <linux/kernel.h>

#include <linux/module.h>

#include <linux/list_lru.h>

bool list_lru_add(struct list_lru *lru, struct list_head *item)

{

	spin_lock(&lru->lock);

	if (list_empty(item)) {

		list_add_tail(item, &lru->list);

		lru->nr_items++;

		spin_unlock(&lru->lock);

		return true;

	}

	spin_unlock(&lru->lock);

	return false;

}

EXPORT_SYMBOL_GPL(list_lru_add);

bool list_lru_del(struct list_lru *lru, struct list_head *item)

{

	spin_lock(&lru->lock);

	if (!list_empty(item)) {

		list_del_init(item);

		lru->nr_items--;

		spin_unlock(&lru->lock);

		return true;

	}

	spin_unlock(&lru->lock);

	return false;

}

EXPORT_SYMBOL_GPL(list_lru_del);

unsigned long list_lru_walk(struct list_lru *lru, list_lru_walk_cb isolate,

			    void *cb_arg, unsigned long nr_to_walk)

{

	struct list_head *item, *n;

	unsigned long removed = 0;

	/*

	 * If we don't keep state of at which pass we are, we can loop at

	 * LRU_RETRY, since we have no guarantees that the caller will be able

	 * to do something other than retry on the next pass. We handle this by

	 * allowing at most one retry per object. This should not be altered

	 * by any condition other than LRU_RETRY.

	 */

	bool first_pass = true;

	spin_lock(&lru->lock);

restart:

	list_for_each_safe(item, n, &lru->list) {

		enum lru_status ret;

		ret = isolate(item, &lru->lock, cb_arg);

		switch (ret) {

		case LRU_REMOVED:

			lru->nr_items--;

			removed++;

			break;

		case LRU_ROTATE:

			list_move_tail(item, &lru->list);

			break;

		case LRU_SKIP:

			break;

		case LRU_RETRY:

			if (!first_pass) {

				first_pass = true;

				break;

			}

			first_pass = false;

			goto restart;

		default:

			BUG();

		}

		if (nr_to_walk-- == 0)

			break;

	}

	spin_unlock(&lru->lock);

	return removed;

}

EXPORT_SYMBOL_GPL(list_lru_walk);

unsigned long list_lru_dispose_all(struct list_lru *lru,

				   list_lru_dispose_cb dispose)

{

	unsigned long disposed = 0;

	LIST_HEAD(dispose_list);

	spin_lock(&lru->lock);

	while (!list_empty(&lru->list)) {

		list_splice_init(&lru->list, &dispose_list);

		disposed += lru->nr_items;

		lru->nr_items = 0;

		spin_unlock(&lru->lock);

		dispose(&dispose_list);

		spin_lock(&lru->lock);

	}

	spin_unlock(&lru->lock);

	return disposed;

}

int list_lru_init(struct list_lru *lru)

{

	spin_lock_init(&lru->lock);

	INIT_LIST_HEAD(&lru->list);

	lru->nr_items = 0;

	return 0;

}

EXPORT_SYMBOL_GPL(list_lru_init);