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>

3 files changed, 233 insertions, 1 deletions

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
new file mode 100644
index 000000000000..1a548b0b7578
--- /dev/null
+++ b/include/linux/list_lru.h
@@ -0,0 +1,115 @@
+/*
+ * 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 */
diff --git a/mm/Makefile b/mm/Makefile
index f00803386a67..305d10acd081 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -17,7 +17,7 @@ obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
                            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
 
diff --git a/mm/list_lru.c b/mm/list_lru.c
new file mode 100644
index 000000000000..dd74c5434cd8
--- /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);