list: add a new LRU list type

Several subsystems use the same construct for LRU lists - a list head, a
spin lock and and item count.  They also use exactly the same code for
adding and removing items from the LRU.  Create a generic type for these
LRU lists.

This is the beginning of generic, node aware LRUs for shrinkers to work
with.

[glommer@openvz.org: enum defined constants for lru. Suggested by gthelen, don't relock over retry]
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Glauber Costa <glommer@openvz.org>
Reviewed-by: Greg Thelen <gthelen@google.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Carlos Maiolino <cmaiolino@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Rientjes <rientjes@google.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: J. Bruce Fields <bfields@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Kent Overstreet <koverstreet@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 117 insertions, 0 deletions

diff --git a/mm/list_lru.c b/mm/list_lru.c
new file mode 100644
index 0000000..dd74c54
--- /dev/null
+++ b/mm/list_lru.c
@@ -0,0 +1,117 @@
+/*
+ * 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);