drm: implement helper functions for scanning lru list

These helper functions can be used to efficiently scan lru list
for eviction. Eviction becomes a three stage process:
1. Scanning through the lru list until a suitable hole has been found.
2. Scan backwards to restore drm_mm consistency and find out which
   objects fall into the hole.
3. Evict the objects that fall into the hole.

These helper functions don't allocate any memory (at the price of
not allowing any other concurrent operations). Hence this can also be
used for ttm (which does lru scanning under a spinlock).

Evicting objects in this fashion should be more fair than the current
approach by i915 (scan the lru for a object large enough to contain
the new object). It's also more efficient than the current approach used
by ttm (uncoditionally evict objects from the lru until there's enough
free space).

Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Thomas Hellstrom <thellstrom@vmwgfx.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_mm.c

@@ -53,9 +53,9 @@ static struct drm_mm_node *drm_mm_kmalloc(struct drm_mm *mm, int atomic)
 	struct drm_mm_node *child;
 
 	if (atomic)
-		child = kmalloc(sizeof(*child), GFP_ATOMIC);
+		child = kzalloc(sizeof(*child), GFP_ATOMIC);
 	else
-		child = kmalloc(sizeof(*child), GFP_KERNEL);
+		child = kzalloc(sizeof(*child), GFP_KERNEL);
 
 	if (unlikely(child == NULL)) {
 		spin_lock(&mm->unused_lock);
@@ -85,7 +85,7 @@ int drm_mm_pre_get(struct drm_mm *mm)
 	spin_lock(&mm->unused_lock);
 	while (mm->num_unused < MM_UNUSED_TARGET) {
 		spin_unlock(&mm->unused_lock);
-		node = kmalloc(sizeof(*node), GFP_KERNEL);
+		node = kzalloc(sizeof(*node), GFP_KERNEL);
 		spin_lock(&mm->unused_lock);
 
 		if (unlikely(node == NULL)) {
@@ -134,7 +134,6 @@ static struct drm_mm_node *drm_mm_split_at_start(struct drm_mm_node *parent,
 
 	INIT_LIST_HEAD(&child->free_stack);
 
-	child->free = 0;
 	child->size = size;
 	child->start = parent->start;
 	child->mm = parent->mm;
@@ -235,6 +234,9 @@ void drm_mm_put_block(struct drm_mm_node *cur)
 
 	int merged = 0;
 
+	BUG_ON(cur->scanned_block || cur->scanned_prev_free
+				  || cur->scanned_next_free);
+
 	if (cur_head->prev != root_head) {
 		prev_node =
 		    list_entry(cur_head->prev, struct drm_mm_node, node_list);
@@ -312,6 +314,8 @@ struct drm_mm_node *drm_mm_search_free(const struct drm_mm *mm,
 	struct drm_mm_node *best;
 	unsigned long best_size;
 
+	BUG_ON(mm->scanned_blocks);
+
 	best = NULL;
 	best_size = ~0UL;
 
@@ -343,6 +347,8 @@ struct drm_mm_node *drm_mm_search_free_in_range(const struct drm_mm *mm,
 	struct drm_mm_node *best;
 	unsigned long best_size;
 
+	BUG_ON(mm->scanned_blocks);
+
 	best = NULL;
 	best_size = ~0UL;
 
@@ -366,6 +372,158 @@ struct drm_mm_node *drm_mm_search_free_in_range(const struct drm_mm *mm,
 }
 EXPORT_SYMBOL(drm_mm_search_free_in_range);
 
+/**
+ * Initializa lru scanning.
+ *
+ * This simply sets up the scanning routines with the parameters for the desired
+ * hole.
+ *
+ * Warning: As long as the scan list is non-empty, no other operations than
+ * adding/removing nodes to/from the scan list are allowed.
+ */
+void drm_mm_init_scan(struct drm_mm *mm, unsigned long size,
+		      unsigned alignment)
+{
+	mm->scan_alignment = alignment;
+	mm->scan_size = size;
+	mm->scanned_blocks = 0;
+	mm->scan_hit_start = 0;
+	mm->scan_hit_size = 0;
+}
+EXPORT_SYMBOL(drm_mm_init_scan);
+
+/**
+ * Add a node to the scan list that might be freed to make space for the desired
+ * hole.
+ *
+ * Returns non-zero, if a hole has been found, zero otherwise.
+ */
+int drm_mm_scan_add_block(struct drm_mm_node *node)
+{
+	struct drm_mm *mm = node->mm;
+	struct list_head *prev_free, *next_free;
+	struct drm_mm_node *prev_node, *next_node;
+
+	mm->scanned_blocks++;
+
+	prev_free = next_free = NULL;
+
+	BUG_ON(node->free);
+	node->scanned_block = 1;
+	node->free = 1;
+
+	if (node->node_list.prev != &mm->node_list) {
+		prev_node = list_entry(node->node_list.prev, struct drm_mm_node,
+				       node_list);
+
+		if (prev_node->free) {
+			list_del(&prev_node->node_list);
+
+			node->start = prev_node->start;
+			node->size += prev_node->size;
+
+			prev_node->scanned_prev_free = 1;
+
+			prev_free = &prev_node->free_stack;
+		}
+	}
+
+	if (node->node_list.next != &mm->node_list) {
+		next_node = list_entry(node->node_list.next, struct drm_mm_node,
+				       node_list);
+
+		if (next_node->free) {
+			list_del(&next_node->node_list);
+
+			node->size += next_node->size;
+
+			next_node->scanned_next_free = 1;
+
+			next_free = &next_node->free_stack;
+		}
+	}
+
+	/* The free_stack list is not used for allocated objects, so these two
+	 * pointers can be abused (as long as no allocations in this memory
+	 * manager happens). */
+	node->free_stack.prev = prev_free;
+	node->free_stack.next = next_free;
+
+	if (check_free_mm_node(node, mm->scan_size, mm->scan_alignment)) {
+		mm->scan_hit_start = node->start;
+		mm->scan_hit_size = node->size;
+
+		return 1;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_mm_scan_add_block);
+
+/**
+ * Remove a node from the scan list.
+ *
+ * Nodes _must_ be removed in the exact same order from the scan list as they
+ * have been added, otherwise the internal state of the memory manager will be
+ * corrupted.
+ *
+ * When the scan list is empty, the selected memory nodes can be freed. An
+ * immediatly following drm_mm_search_free with best_match = 0 will then return
+ * the just freed block (because its at the top of the free_stack list).
+ *
+ * Returns one if this block should be evicted, zero otherwise. Will always
+ * return zero when no hole has been found.
+ */
+int drm_mm_scan_remove_block(struct drm_mm_node *node)
+{
+	struct drm_mm *mm = node->mm;
+	struct drm_mm_node *prev_node, *next_node;
+
+	mm->scanned_blocks--;
+
+	BUG_ON(!node->scanned_block);
+	node->scanned_block = 0;
+	node->free = 0;
+
+	prev_node = list_entry(node->free_stack.prev, struct drm_mm_node,
+			       free_stack);
+	next_node = list_entry(node->free_stack.next, struct drm_mm_node,
+			       free_stack);
+
+	if (prev_node) {
+		BUG_ON(!prev_node->scanned_prev_free);
+		prev_node->scanned_prev_free = 0;
+
+		list_add_tail(&prev_node->node_list, &node->node_list);
+
+		node->start = prev_node->start + prev_node->size;
+		node->size -= prev_node->size;
+	}
+
+	if (next_node) {
+		BUG_ON(!next_node->scanned_next_free);
+		next_node->scanned_next_free = 0;
+
+		list_add(&next_node->node_list, &node->node_list);
+
+		node->size -= next_node->size;
+	}
+
+	INIT_LIST_HEAD(&node->free_stack);
+
+	/* Only need to check for containement because start&size for the
+	 * complete resulting free block (not just the desired part) is
+	 * stored. */
+	if (node->start >= mm->scan_hit_start &&
+	    node->start + node->size
+	    		<= mm->scan_hit_start + mm->scan_hit_size) {
+		return 1;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_mm_scan_remove_block);
+
 int drm_mm_clean(struct drm_mm * mm)
 {
 	struct list_head *head = &mm->node_list;
@@ -380,6 +538,7 @@ int drm_mm_init(struct drm_mm * mm, unsigned long start, unsigned long size)
 	INIT_LIST_HEAD(&mm->free_stack);
 	INIT_LIST_HEAD(&mm->unused_nodes);
 	mm->num_unused = 0;
+	mm->scanned_blocks = 0;
 	spin_lock_init(&mm->unused_lock);
 
 	return drm_mm_create_tail_node(mm, start, size, 0);

include/drm/drm_mm.h

@@ -44,7 +44,10 @@
 struct drm_mm_node {
 	struct list_head free_stack;
 	struct list_head node_list;
-	int free;
+	unsigned free : 1;
+	unsigned scanned_block : 1;
+	unsigned scanned_prev_free : 1;
+	unsigned scanned_next_free : 1;
 	unsigned long start;
 	unsigned long size;
 	struct drm_mm *mm;
@@ -59,6 +62,11 @@ struct drm_mm {
 	struct list_head unused_nodes;
 	int num_unused;
 	spinlock_t unused_lock;
+	unsigned scan_alignment;
+	unsigned long scan_size;
+	unsigned long scan_hit_start;
+	unsigned scan_hit_size;
+	unsigned scanned_blocks;
 };
 
 /*
@@ -135,6 +143,11 @@ static inline struct drm_mm *drm_get_mm(struct drm_mm_node *block)
 	return block->mm;
 }
 
+void drm_mm_init_scan(struct drm_mm *mm, unsigned long size,
+		      unsigned alignment);
+int drm_mm_scan_add_block(struct drm_mm_node *node);
+int drm_mm_scan_remove_block(struct drm_mm_node *node);
+
 extern void drm_mm_debug_table(struct drm_mm *mm, const char *prefix);
 #ifdef CONFIG_DEBUG_FS
 int drm_mm_dump_table(struct seq_file *m, struct drm_mm *mm);