DRBD: lru_cache

The lru_cache is a fixed size cache of equal sized objects. It allows its
users to do arbitrary transactions in case an element in the cache needs to
be replaced. Its replacement policy is LRU.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/lru_cache.h

+/*
+   lru_cache.c
+
+   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
+
+   Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
+   Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
+   Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
+
+   drbd is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   drbd is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with drbd; see the file COPYING.  If not, write to
+   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+ */
+
+#ifndef LRU_CACHE_H
+#define LRU_CACHE_H
+
+#include <linux/list.h>
+
+struct lc_element {
+	struct hlist_node colision;
+	struct list_head list;		 /* LRU list or free list */
+	unsigned int refcnt;
+	unsigned int lc_number;
+};
+
+struct lru_cache {
+	struct list_head lru;
+	struct list_head free;
+	struct list_head in_use;
+	size_t element_size;
+	unsigned int  nr_elements;
+	unsigned int  new_number;
+
+	unsigned int used;
+	unsigned long flags;
+	unsigned long hits, misses, starving, dirty, changed;
+	struct lc_element *changing_element; /* just for paranoia */
+
+	void  *lc_private;
+	const char *name;
+
+	struct hlist_head slot[0];
+	/* hash colision chains here, then element storage. */
+};
+
+
+/* flag-bits for lru_cache */
+enum {
+	__LC_PARANOIA,
+	__LC_DIRTY,
+	__LC_STARVING,
+};
+#define LC_PARANOIA (1<<__LC_PARANOIA)
+#define LC_DIRTY    (1<<__LC_DIRTY)
+#define LC_STARVING (1<<__LC_STARVING)
+
+extern struct lru_cache *lc_alloc(const char *name, unsigned int e_count,
+				  size_t e_size, void *private_p);
+extern void lc_reset(struct lru_cache *lc);
+extern void lc_free(struct lru_cache *lc);
+extern void lc_set(struct lru_cache *lc, unsigned int enr, int index);
+extern void lc_del(struct lru_cache *lc, struct lc_element *element);
+
+extern struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr);
+extern struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr);
+extern struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr);
+extern unsigned int lc_put(struct lru_cache *lc, struct lc_element *e);
+extern void lc_changed(struct lru_cache *lc, struct lc_element *e);
+
+struct seq_file;
+extern size_t lc_printf_stats(struct seq_file *seq, struct lru_cache *lc);
+
+void lc_dump(struct lru_cache *lc, struct seq_file *seq, char *utext,
+	     void (*detail) (struct seq_file *, struct lc_element *));
+
+/* This can be used to stop lc_get from changing the set of active elements.
+ * Note that the reference counts and order on the lru list may still change.
+ * returns true if we aquired the lock.
+ */
+static inline int lc_try_lock(struct lru_cache *lc)
+{
+	return !test_and_set_bit(__LC_DIRTY, &lc->flags);
+}
+
+static inline void lc_unlock(struct lru_cache *lc)
+{
+	clear_bit(__LC_DIRTY, &lc->flags);
+	smp_mb__after_clear_bit();
+}
+
+static inline int lc_is_used(struct lru_cache *lc, unsigned int enr)
+{
+	struct lc_element *e = lc_find(lc, enr);
+	return e && e->refcnt;
+}
+
+#define LC_FREE (-1U)
+
+#define lc_e_base(lc)  ((char *)((lc)->slot + (lc)->nr_elements))
+#define lc_entry(lc, i) ((struct lc_element *) \
+		       (lc_e_base(lc) + (i)*(lc)->element_size))
+#define lc_index_of(lc, e) (((char *)(e) - lc_e_base(lc))/(lc)->element_size)
+
+#endif