[PATCH v4 1/3] mm/vmap: keep track of free blocks for vmap allocation

[Uladzislau Rezki (Sony)]

Currently an allocation of the new vmap area is done over busy
list iteration(complexity O(n)) until a suitable hole is found
between two busy areas. Therefore each new allocation causes
the list being grown. Due to over fragmented list and different
permissive parameters an allocation can take a long time. For
example on embedded devices it is milliseconds.

This patch organizes the KVA memory layout into free areas of the
1-ULONG_MAX range. It uses an augment red-black tree that keeps
blocks sorted by their offsets in pair with linked list keeping
the free space in order of increasing addresses.

Nodes are augmented with the size of the maximum available free
block in its left or right sub-tree. Thus, that allows to take a
decision and traversal toward the block that will fit and will
have the lowest start address, i.e. it is sequential allocation.

Allocation: to allocate a new block a search is done over the
tree until a suitable lowest(left most) block is large enough
to encompass: the requested size, alignment and vstart point.
If the block is bigger than requested size - it is split.

De-allocation: when a busy vmap area is freed it can either be
merged or inserted to the tree. Red-black tree allows efficiently
find a spot whereas a linked list provides a constant-time access
to previous and next blocks to check if merging can be done. In case
of merging of de-allocated memory chunk a large coalesced area is
created.

Complexity: ~O(log(N))

Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
---
 include/linux/vmalloc.h |    6 +-
 mm/vmalloc.c            | 1004 +++++++++++++++++++++++++++++++++++------------
 2 files changed, 763 insertions(+), 247 deletions(-)

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 398e9c95cd61..ad483378fdd1 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -45,12 +45,16 @@ struct vm_struct {
 struct vmap_area {
 	unsigned long va_start;
 	unsigned long va_end;
+
+	/*
+	 * Largest available free size in subtree.
+	 */
+	unsigned long subtree_max_size;
 	unsigned long flags;
 	struct rb_node rb_node;         /* address sorted rbtree */
 	struct list_head list;          /* address sorted list */
 	struct llist_node purge_list;    /* "lazy purge" list */
 	struct vm_struct *vm;
-	struct rcu_head rcu_head;
 };
 
 /*
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index b7455d4c8c12..c6f9d0637464 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -31,6 +31,7 @@
 #include <linux/compiler.h>
 #include <linux/llist.h>
 #include <linux/bitops.h>
+#include <linux/rbtree_augmented.h>
 
 #include <linux/uaccess.h>
 #include <asm/tlbflush.h>
@@ -331,14 +332,67 @@ static DEFINE_SPINLOCK(vmap_area_lock);
 LIST_HEAD(vmap_area_list);
 static LLIST_HEAD(vmap_purge_list);
 static struct rb_root vmap_area_root = RB_ROOT;
+static bool vmap_initialized __read_mostly;
 
-/* The vmap cache globals are protected by vmap_area_lock */
-static struct rb_node *free_vmap_cache;
-static unsigned long cached_hole_size;
-static unsigned long cached_vstart;
-static unsigned long cached_align;
+/*
+ * This kmem_cache is used for vmap_area objects. Instead of
+ * allocating from slab we reuse an object from this cache to
+ * make things faster. Especially in "no edge" splitting of
+ * free block.
+ */
+static struct kmem_cache *vmap_area_cachep;
+
+/*
+ * This linked list is used in pair with free_vmap_area_root.
+ * It gives O(1) access to prev/next to perform fast coalescing.
+ */
+static LIST_HEAD(free_vmap_area_list);
+
+/*
+ * This augment red-black tree represents the free vmap space.
+ * All vmap_area objects in this tree are sorted by va->va_start
+ * address. It is used for allocation and merging when a vmap
+ * object is released.
+ *
+ * Each vmap_area node contains a maximum available free block
+ * of its sub-tree, right or left. Therefore it is possible to
+ * find a lowest match of free area.
+ */
+static struct rb_root free_vmap_area_root = RB_ROOT;
+
+static __always_inline unsigned long
+va_size(struct vmap_area *va)
+{
+	return (va->va_end - va->va_start);
+}
+
+static __always_inline unsigned long
+get_subtree_max_size(struct rb_node *node)
+{
+	struct vmap_area *va;
+
+	va = rb_entry_safe(node, struct vmap_area, rb_node);
+	return va ? va->subtree_max_size : 0;
+}
 
-static unsigned long vmap_area_pcpu_hole;
+/*
+ * Gets called when remove the node and rotate.
+ */
+static __always_inline unsigned long
+compute_subtree_max_size(struct vmap_area *va)
+{
+	return max3(va_size(va),
+		get_subtree_max_size(va->rb_node.rb_left),
+		get_subtree_max_size(va->rb_node.rb_right));
+}
+
+RB_DECLARE_CALLBACKS(static, free_vmap_area_rb_augment_cb,
+	struct vmap_area, rb_node, unsigned long, subtree_max_size,
+	compute_subtree_max_size)
+
+static void purge_vmap_area_lazy(void);
+static BLOCKING_NOTIFIER_HEAD(vmap_notify_list);
+static unsigned long lazy_max_pages(void);
 
 static struct vmap_area *__find_vmap_area(unsigned long addr)
 {
@@ -359,41 +413,522 @@ static struct vmap_area *__find_vmap_area(unsigned long addr)
 	return NULL;
 }
 
-static void __insert_vmap_area(struct vmap_area *va)
-{
-	struct rb_node **p = &vmap_area_root.rb_node;
-	struct rb_node *parent = NULL;
-	struct rb_node *tmp;
+/*
+ * This function returns back addresses of parent node
+ * and its left or right link for further processing.
+ */
+static __always_inline struct rb_node **
+find_va_links(struct vmap_area *va,
+	struct rb_root *root, struct rb_node *from,
+	struct rb_node **parent)
+{
+	struct vmap_area *tmp_va;
+	struct rb_node **link;
+
+	if (root) {
+		link = &root->rb_node;
+		if (unlikely(!*link)) {
+			*parent = NULL;
+			return link;
+		}
+	} else {
+		link = &from;
+	}
 
-	while (*p) {
-		struct vmap_area *tmp_va;
+	/*
+	 * Go to the bottom of the tree. When we hit the last point
+	 * we end up with parent rb_node and correct direction, i name
+	 * it link, where the new va->rb_node will be attached to.
+	 */
+	do {
+		tmp_va = rb_entry(*link, struct vmap_area, rb_node);
 
-		parent = *p;
-		tmp_va = rb_entry(parent, struct vmap_area, rb_node);
-		if (va->va_start < tmp_va->va_end)
-			p = &(*p)->rb_left;
-		else if (va->va_end > tmp_va->va_start)
-			p = &(*p)->rb_right;
+		/*
+		 * During the traversal we also do some sanity check.
+		 * Trigger the BUG() if there are sides(left/right)
+		 * or full overlaps.
+		 */
+		if (va->va_start < tmp_va->va_end &&
+				va->va_end <= tmp_va->va_start)
+			link = &(*link)->rb_left;
+		else if (va->va_end > tmp_va->va_start &&
+				va->va_start >= tmp_va->va_end)
+			link = &(*link)->rb_right;
 		else
 			BUG();
+	} while (*link);
+
+	*parent = &tmp_va->rb_node;
+	return link;
+}
+
+static __always_inline struct list_head *
+get_va_next_sibling(struct rb_node *parent, struct rb_node **link)
+{
+	struct list_head *list;
+
+	if (unlikely(!parent))
+		/*
+		 * The red-black tree where we try to find VA neighbors
+		 * before merging or inserting is empty, i.e. it means
+		 * there is no free vmap space. Normally it does not
+		 * happen but we handle this case anyway.
+		 */
+		return NULL;
+
+	list = &rb_entry(parent, struct vmap_area, rb_node)->list;
+	return (&parent->rb_right == link ? list->next : list);
+}
+
+static __always_inline void
+link_va(struct vmap_area *va, struct rb_root *root,
+	struct rb_node *parent, struct rb_node **link, struct list_head *head)
+{
+	/*
+	 * VA is still not in the list, but we can
+	 * identify its future previous list_head node.
+	 */
+	if (likely(parent)) {
+		head = &rb_entry(parent, struct vmap_area, rb_node)->list;
+		if (&parent->rb_right != link)
+			head = head->prev;
 	}
 
-	rb_link_node(&va->rb_node, parent, p);
-	rb_insert_color(&va->rb_node, &vmap_area_root);
+	/* Insert to the rb-tree */
+	rb_link_node(&va->rb_node, parent, link);
+	if (root == &free_vmap_area_root) {
+		/*
+		 * Some explanation here. Just perform simple insertion
+		 * to the tree. We do not set va->subtree_max_size to
+		 * its current size before calling rb_insert_augmented().
+		 * It is because of we populate the tree from the bottom
+		 * to parent levels when the node _is_ in the tree.
+		 *
+		 * Therefore we set subtree_max_size to zero after insertion,
+		 * to let __augment_tree_propagate_from() puts everything to
+		 * the correct order later on.
+		 */
+		rb_insert_augmented(&va->rb_node,
+			root, &free_vmap_area_rb_augment_cb);
+		va->subtree_max_size = 0;
+	} else {
+		rb_insert_color(&va->rb_node, root);
+	}
 
-	/* address-sort this list */
-	tmp = rb_prev(&va->rb_node);
-	if (tmp) {
-		struct vmap_area *prev;
-		prev = rb_entry(tmp, struct vmap_area, rb_node);
-		list_add_rcu(&va->list, &prev->list);
-	} else
-		list_add_rcu(&va->list, &vmap_area_list);
+	/* Address-sort this list */
+	list_add(&va->list, head);
 }
 
-static void purge_vmap_area_lazy(void);
+static __always_inline void
+unlink_va(struct vmap_area *va, struct rb_root *root)
+{
+	/*
+	 * During merging a VA node can be empty, therefore
+	 * not linked with the tree nor list. Just check it.
+	 */
+	if (!RB_EMPTY_NODE(&va->rb_node)) {
+		if (root == &free_vmap_area_root)
+			rb_erase_augmented(&va->rb_node,
+				root, &free_vmap_area_rb_augment_cb);
+		else
+			rb_erase(&va->rb_node, root);
 
-static BLOCKING_NOTIFIER_HEAD(vmap_notify_list);
+		list_del(&va->list);
+		RB_CLEAR_NODE(&va->rb_node);
+	}
+}
+
+/*
+ * This function populates subtree_max_size from bottom to upper
+ * levels starting from VA point. The propagation must be done
+ * when VA size is modified by changing its va_start/va_end. Or
+ * in case of newly inserting of VA to the tree.
+ *
+ * It means that __augment_tree_propagate_from() must be called:
+ * - After VA has been inserted to the tree(free path);
+ * - After VA has been shrunk(allocation path);
+ * - After VA has been increased(merging path).
+ *
+ * Please note that, it does not mean that upper parent nodes
+ * and their subtree_max_size are recalculated all the time up
+ * to the root node.
+ *
+ *       4--8
+ *        /\
+ *       /  \
+ *      /    \
+ *    2--2  8--8
+ *
+ * For example if we modify the node 4, shrinking it to 2, then
+ * no any modification is required. If we shrink the node 2 to 1
+ * its subtree_max_size is updated only, and set to 1. If we shrink
+ * the node 8 to 6, then its subtree_max_size is set to 6 and parent
+ * node becomes 4--6.
+ */
+static __always_inline void
+augment_tree_propagate_from(struct vmap_area *va)
+{
+	struct rb_node *node = &va->rb_node;
+	unsigned long new_va_sub_max_size;
+
+	while (node) {
+		va = rb_entry(node, struct vmap_area, rb_node);
+		new_va_sub_max_size = compute_subtree_max_size(va);
+
+		/*
+		 * If the newly calculated maximum available size of the
+		 * subtree is equal to the current one, then it means that
+		 * the tree is propagated correctly. So we have to stop at
+		 * this point to save cycles.
+		 */
+		if (va->subtree_max_size == new_va_sub_max_size)
+			break;
+
+		va->subtree_max_size = new_va_sub_max_size;
+		node = rb_parent(&va->rb_node);
+	}
+}
+
+static void
+insert_vmap_area(struct vmap_area *va,
+	struct rb_root *root, struct list_head *head)
+{
+	struct rb_node **link;
+	struct rb_node *parent;
+
+	link = find_va_links(va, root, NULL, &parent);
+	link_va(va, root, parent, link, head);
+}
+
+static void
+insert_vmap_area_augment(struct vmap_area *va,
+	struct rb_node *from, struct rb_root *root,
+	struct list_head *head)
+{
+	struct rb_node **link;
+	struct rb_node *parent;
+
+	if (from)
+		link = find_va_links(va, NULL, from, &parent);
+	else
+		link = find_va_links(va, root, NULL, &parent);
+
+	link_va(va, root, parent, link, head);
+	augment_tree_propagate_from(va);
+}
+
+/*
+ * Merge de-allocated chunk of VA memory with previous
+ * and next free blocks. If coalesce is not done a new
+ * free area is inserted. If VA has been merged, it is
+ * freed.
+ */
+static __always_inline void
+merge_or_add_vmap_area(struct vmap_area *va,
+	struct rb_root *root, struct list_head *head)
+{
+	struct vmap_area *sibling;
+	struct list_head *next;
+	struct rb_node **link;
+	struct rb_node *parent;
+	bool merged = false;
+
+	/*
+	 * Find a place in the tree where VA potentially will be
+	 * inserted, unless it is merged with its sibling/siblings.
+	 */
+	link = find_va_links(va, root, NULL, &parent);
+
+	/*
+	 * Get next node of VA to check if merging can be done.
+	 */
+	next = get_va_next_sibling(parent, link);
+	if (unlikely(next == NULL))
+		goto insert;
+
+	/*
+	 * start            end
+	 * |                |
+	 * |<------VA------>|<-----Next----->|
+	 *                  |                |
+	 *                  start            end
+	 */
+	if (next != head) {
+		sibling = list_entry(next, struct vmap_area, list);
+		if (sibling->va_start == va->va_end) {
+			sibling->va_start = va->va_start;
+
+			/* Check and update the tree if needed. */
+			augment_tree_propagate_from(sibling);
+
+			/* Remove this VA, it has been merged. */
+			unlink_va(va, root);
+
+			/* Free vmap_area object. */
+			kmem_cache_free(vmap_area_cachep, va);
+
+			/* Point to the new merged area. */
+			va = sibling;
+			merged = true;
+		}
+	}
+
+	/*
+	 * start            end
+	 * |                |
+	 * |<-----Prev----->|<------VA------>|
+	 *                  |                |
+	 *                  start            end
+	 */
+	if (next->prev != head) {
+		sibling = list_entry(next->prev, struct vmap_area, list);
+		if (sibling->va_end == va->va_start) {
+			sibling->va_end = va->va_end;
+
+			/* Check and update the tree if needed. */
+			augment_tree_propagate_from(sibling);
+
+			/* Remove this VA, it has been merged. */
+			unlink_va(va, root);
+
+			/* Free vmap_area object. */
+			kmem_cache_free(vmap_area_cachep, va);
+
+			return;
+		}
+	}
+
+insert:
+	if (!merged) {
+		link_va(va, root, parent, link, head);
+		augment_tree_propagate_from(va);
+	}
+}
+
+static __always_inline bool
+is_within_this_va(struct vmap_area *va, unsigned long size,
+	unsigned long align, unsigned long vstart)
+{
+	unsigned long nva_start_addr;
+
+	if (va->va_start > vstart)
+		nva_start_addr = ALIGN(va->va_start, align);
+	else
+		nva_start_addr = ALIGN(vstart, align);
+
+	/* Can be overflowed due to big size or alignment. */
+	if (nva_start_addr + size < nva_start_addr ||
+			nva_start_addr < vstart)
+		return false;
+
+	return (nva_start_addr + size <= va->va_end);
+}
+
+/*
+ * Find the first free block(lowest start address) in the tree,
+ * that will accomplish the request corresponding to passing
+ * parameters.
+ */
+static __always_inline struct vmap_area *
+find_vmap_lowest_match(unsigned long size,
+	unsigned long align, unsigned long vstart)
+{
+	struct vmap_area *va;
+	struct rb_node *node;
+	unsigned long length;
+
+	/* Start from the root. */
+	node = free_vmap_area_root.rb_node;
+
+	/* Adjust the search size for alignment overhead. */
+	length = size + align - 1;
+
+	while (node) {
+		va = rb_entry(node, struct vmap_area, rb_node);
+
+		if (get_subtree_max_size(node->rb_left) >= length &&
+				vstart < va->va_start) {
+			node = node->rb_left;
+		} else {
+			if (is_within_this_va(va, size, align, vstart))
+				return va;
+
+			/*
+			 * Does not make sense to go deeper towards the right
+			 * sub-tree if it does not have a free block that is
+			 * equal or bigger to the requested search length.
+			 */
+			if (get_subtree_max_size(node->rb_right) >= length) {
+				node = node->rb_right;
+				continue;
+			}
+
+			/*
+			 * OK. We roll back and find the fist right sub-tree,
+			 * that will satisfy the search criteria. It can happen
+			 * only once due to "vstart" restriction.
+			 */
+			while ((node = rb_parent(node))) {
+				va = rb_entry(node, struct vmap_area, rb_node);
+				if (is_within_this_va(va, size, align, vstart))
+					return va;
+
+				if (get_subtree_max_size(node->rb_right) >= length &&
+						vstart <= va->va_start) {
+					node = node->rb_right;
+					break;
+				}
+			}
+		}
+	}
+
+	return NULL;
+}
+
+enum fit_type {
+	NOTHING_FIT = 0,
+	FL_FIT_TYPE = 1,	/* full fit */
+	LE_FIT_TYPE = 2,	/* left edge fit */
+	RE_FIT_TYPE = 3,	/* right edge fit */
+	NE_FIT_TYPE = 4		/* no edge fit */
+};
+
+static __always_inline enum fit_type
+classify_va_fit_type(struct vmap_area *va,
+	unsigned long nva_start_addr, unsigned long size)
+{
+	enum fit_type type;
+
+	/* Check if it is within VA. */
+	if (nva_start_addr < va->va_start ||
+			nva_start_addr + size > va->va_end)
+		return NOTHING_FIT;
+
+	/* Now classify. */
+	if (va->va_start == nva_start_addr) {
+		if (va->va_end == nva_start_addr + size)
+			type = FL_FIT_TYPE;
+		else
+			type = LE_FIT_TYPE;
+	} else if (va->va_end == nva_start_addr + size) {
+		type = RE_FIT_TYPE;
+	} else {
+		type = NE_FIT_TYPE;
+	}
+
+	return type;
+}
+
+static __always_inline int
+adjust_va_to_fit_type(struct vmap_area *va,
+	unsigned long nva_start_addr, unsigned long size,
+	enum fit_type type)
+{
+	struct vmap_area *lva;
+
+	if (type == FL_FIT_TYPE) {
+		/*
+		 * No need to split VA, it fully fits.
+		 *
+		 * |               |
+		 * V      NVA      V
+		 * |---------------|
+		 */
+		unlink_va(va, &free_vmap_area_root);
+		kmem_cache_free(vmap_area_cachep, va);
+	} else if (type == LE_FIT_TYPE) {
+		/*
+		 * Split left edge of fit VA.
+		 *
+		 * |       |
+		 * V  NVA  V   R
+		 * |-------|-------|
+		 */
+		va->va_start += size;
+	} else if (type == RE_FIT_TYPE) {
+		/*
+		 * Split right edge of fit VA.
+		 *
+		 *         |       |
+		 *     L   V  NVA  V
+		 * |-------|-------|
+		 */
+		va->va_end = nva_start_addr;
+	} else if (type == NE_FIT_TYPE) {
+		/*
+		 * Split no edge of fit VA.
+		 *
+		 *     |       |
+		 *   L V  NVA  V R
+		 * |---|-------|---|
+		 */
+		lva = kmem_cache_alloc(vmap_area_cachep, GFP_NOWAIT);
+		if (unlikely(!lva))
+			return -1;
+
+		/*
+		 * Build the remainder.
+		 */
+		lva->va_start = va->va_start;
+		lva->va_end = nva_start_addr;
+
+		/*
+		 * Shrink this VA to remaining size.
+		 */
+		va->va_start = nva_start_addr + size;
+	} else {
+		return -1;
+	}
+
+	if (type != FL_FIT_TYPE) {
+		augment_tree_propagate_from(va);
+
+		if (type == NE_FIT_TYPE)
+			insert_vmap_area_augment(lva, &va->rb_node,
+				&free_vmap_area_root, &free_vmap_area_list);
+	}
+
+	return 0;
+}
+
+/*
+ * Returns a start address of the newly allocated area, if success.
+ * Otherwise a vend is returned that indicates failure.
+ */
+static __always_inline unsigned long
+__alloc_vmap_area(unsigned long size, unsigned long align,
+	unsigned long vstart, unsigned long vend, int node)
+{
+	unsigned long nva_start_addr;
+	struct vmap_area *va;
+	enum fit_type type;
+	int ret;
+
+	va = find_vmap_lowest_match(size, align, vstart);
+	if (unlikely(!va))
+		return vend;
+
+	if (va->va_start > vstart)
+		nva_start_addr = ALIGN(va->va_start, align);
+	else
+		nva_start_addr = ALIGN(vstart, align);
+
+	/* Check the "vend" restriction. */
+	if (nva_start_addr + size > vend)
+		return vend;
+
+	/* Classify what we have found. */
+	type = classify_va_fit_type(va, nva_start_addr, size);
+	if (WARN_ON_ONCE(type == NOTHING_FIT))
+		return vend;
+
+	/* Update the free vmap_area. */
+	ret = adjust_va_to_fit_type(va, nva_start_addr, size, type);
+	if (ret)
+		return vend;
+
+	return nva_start_addr;
+}
 
 /*
  * Allocate a region of KVA of the specified size and alignment, within the
@@ -405,18 +940,19 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 				int node, gfp_t gfp_mask)
 {
 	struct vmap_area *va;
-	struct rb_node *n;
 	unsigned long addr;
 	int purged = 0;
-	struct vmap_area *first;
 
 	BUG_ON(!size);
 	BUG_ON(offset_in_page(size));
 	BUG_ON(!is_power_of_2(align));
 
+	if (unlikely(!vmap_initialized))
+		return ERR_PTR(-EBUSY);
+
 	might_sleep();
 
-	va = kmalloc_node(sizeof(struct vmap_area),
+	va = kmem_cache_alloc_node(vmap_area_cachep,
 			gfp_mask & GFP_RECLAIM_MASK, node);
 	if (unlikely(!va))
 		return ERR_PTR(-ENOMEM);
@@ -429,87 +965,20 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 
 retry:
 	spin_lock(&vmap_area_lock);
-	/*
-	 * Invalidate cache if we have more permissive parameters.
-	 * cached_hole_size notes the largest hole noticed _below_
-	 * the vmap_area cached in free_vmap_cache: if size fits
-	 * into that hole, we want to scan from vstart to reuse
-	 * the hole instead of allocating above free_vmap_cache.
-	 * Note that __free_vmap_area may update free_vmap_cache
-	 * without updating cached_hole_size or cached_align.
-	 */
-	if (!free_vmap_cache ||
-			size < cached_hole_size ||
-			vstart < cached_vstart ||
-			align < cached_align) {
-nocache:
-		cached_hole_size = 0;
-		free_vmap_cache = NULL;
-	}
-	/* record if we encounter less permissive parameters */
-	cached_vstart = vstart;
-	cached_align = align;
-
-	/* find starting point for our search */
-	if (free_vmap_cache) {
-		first = rb_entry(free_vmap_cache, struct vmap_area, rb_node);
-		addr = ALIGN(first->va_end, align);
-		if (addr < vstart)
-			goto nocache;
-		if (addr + size < addr)
-			goto overflow;
-
-	} else {
-		addr = ALIGN(vstart, align);
-		if (addr + size < addr)
-			goto overflow;
-
-		n = vmap_area_root.rb_node;
-		first = NULL;
-
-		while (n) {
-			struct vmap_area *tmp;
-			tmp = rb_entry(n, struct vmap_area, rb_node);
-			if (tmp->va_end >= addr) {
-				first = tmp;
-				if (tmp->va_start <= addr)
-					break;
-				n = n->rb_left;
-			} else
-				n = n->rb_right;
-		}
-
-		if (!first)
-			goto found;
-	}
 
-	/* from the starting point, walk areas until a suitable hole is found */
-	while (addr + size > first->va_start && addr + size <= vend) {
-		if (addr + cached_hole_size < first->va_start)
-			cached_hole_size = first->va_start - addr;
-		addr = ALIGN(first->va_end, align);
-		if (addr + size < addr)
-			goto overflow;
-
-		if (list_is_last(&first->list, &vmap_area_list))
-			goto found;
-
-		first = list_next_entry(first, list);
-	}
-
-found:
 	/*
-	 * Check also calculated address against the vstart,
-	 * because it can be 0 because of big align request.
+	 * If an allocation fails, the "vend" address is
+	 * returned. Therefore trigger the overflow path.
 	 */
-	if (addr + size > vend || addr < vstart)
+	addr = __alloc_vmap_area(size, align, vstart, vend, node);
+	if (unlikely(addr == vend))
 		goto overflow;
 
 	va->va_start = addr;
 	va->va_end = addr + size;
 	va->flags = 0;
-	__insert_vmap_area(va);
-	free_vmap_cache = &va->rb_node;
+	insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
+
 	spin_unlock(&vmap_area_lock);
 
 	BUG_ON(!IS_ALIGNED(va->va_start, align));
@@ -538,7 +1007,8 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 	if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit())
 		pr_warn("vmap allocation for size %lu failed: use vmalloc=<size> to increase size\n",
 			size);
-	kfree(va);
+
+	kmem_cache_free(vmap_area_cachep, va);
 	return ERR_PTR(-EBUSY);
 }
 
@@ -558,35 +1028,16 @@ static void __free_vmap_area(struct vmap_area *va)
 {
 	BUG_ON(RB_EMPTY_NODE(&va->rb_node));
 
-	if (free_vmap_cache) {
-		if (va->va_end < cached_vstart) {
-			free_vmap_cache = NULL;
-		} else {
-			struct vmap_area *cache;
-			cache = rb_entry(free_vmap_cache, struct vmap_area, rb_node);
-			if (va->va_start <= cache->va_start) {
-				free_vmap_cache = rb_prev(&va->rb_node);
-				/*
-				 * We don't try to update cached_hole_size or
-				 * cached_align, but it won't go very wrong.
-				 */
-			}
-		}
-	}
-	rb_erase(&va->rb_node, &vmap_area_root);
-	RB_CLEAR_NODE(&va->rb_node);
-	list_del_rcu(&va->list);
-
 	/*
-	 * Track the highest possible candidate for pcpu area
-	 * allocation.  Areas outside of vmalloc area can be returned
-	 * here too, consider only end addresses which fall inside
-	 * vmalloc area proper.
+	 * Remove from the busy tree/list.
 	 */
-	if (va->va_end > VMALLOC_START && va->va_end <= VMALLOC_END)
-		vmap_area_pcpu_hole = max(vmap_area_pcpu_hole, va->va_end);
+	unlink_va(va, &vmap_area_root);
 
-	kfree_rcu(va, rcu_head);
+	/*
+	 * Merge VA with its neighbors, otherwise just add it.
+	 */
+	merge_or_add_vmap_area(va,
+		&free_vmap_area_root, &free_vmap_area_list);
 }
 
 /*
@@ -793,8 +1244,6 @@ static struct vmap_area *find_vmap_area(unsigned long addr)
 
 #define VMAP_BLOCK_SIZE		(VMAP_BBMAP_BITS * PAGE_SIZE)
 
-static bool vmap_initialized __read_mostly = false;
-
 struct vmap_block_queue {
 	spinlock_t lock;
 	struct list_head free;
@@ -1249,12 +1698,58 @@ void __init vm_area_register_early(struct vm_struct *vm, size_t align)
 	vm_area_add_early(vm);
 }
 
+static void vmap_init_free_space(void)
+{
+	unsigned long vmap_start = 1;
+	const unsigned long vmap_end = ULONG_MAX;
+	struct vmap_area *busy, *free;
+
+	/*
+	 *     B     F     B     B     B     F
+	 * -|-----|.....|-----|-----|-----|.....|-
+	 *  |           The KVA space           |
+	 *  |<--------------------------------->|
+	 */
+	list_for_each_entry(busy, &vmap_area_list, list) {
+		if (busy->va_start - vmap_start > 0) {
+			free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
+			if (!WARN_ON_ONCE(!free)) {
+				free->va_start = vmap_start;
+				free->va_end = busy->va_start;
+
+				insert_vmap_area_augment(free, NULL,
+					&free_vmap_area_root,
+						&free_vmap_area_list);
+			}
+		}
+
+		vmap_start = busy->va_end;
+	}
+
+	if (vmap_end - vmap_start > 0) {
+		free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
+		if (!WARN_ON_ONCE(!free)) {
+			free->va_start = vmap_start;
+			free->va_end = vmap_end;
+
+			insert_vmap_area_augment(free, NULL,
+				&free_vmap_area_root,
+					&free_vmap_area_list);
+		}
+	}
+}
+
 void __init vmalloc_init(void)
 {
 	struct vmap_area *va;
 	struct vm_struct *tmp;
 	int i;
 
+	/*
+	 * Create the cache for vmap_area objects.
+	 */
+	vmap_area_cachep = KMEM_CACHE(vmap_area, SLAB_PANIC);
+
 	for_each_possible_cpu(i) {
 		struct vmap_block_queue *vbq;
 		struct vfree_deferred *p;
@@ -1269,16 +1764,21 @@ void __init vmalloc_init(void)
 
 	/* Import existing vmlist entries. */
 	for (tmp = vmlist; tmp; tmp = tmp->next) {
-		va = kzalloc(sizeof(struct vmap_area), GFP_NOWAIT);
+		va = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
+		if (WARN_ON_ONCE(!va))
+			continue;
+
 		va->flags = VM_VM_AREA;
 		va->va_start = (unsigned long)tmp->addr;
 		va->va_end = va->va_start + tmp->size;
 		va->vm = tmp;
-		__insert_vmap_area(va);
+		insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
 	}
 
-	vmap_area_pcpu_hole = VMALLOC_END;
-
+	/*
+	 * Now we can initialize a free vmap space.
+	 */
+	vmap_init_free_space();
 	vmap_initialized = true;
 }
 
@@ -2402,81 +2902,64 @@ static struct vmap_area *node_to_va(struct rb_node *n)
 }
 
 /**
- * pvm_find_next_prev - find the next and prev vmap_area surrounding @end
- * @end: target address
- * @pnext: out arg for the next vmap_area
- * @pprev: out arg for the previous vmap_area
+ * pvm_find_va_enclose_addr - find the vmap_area @addr belongs to
+ * @addr: target address
  *
- * Returns: %true if either or both of next and prev are found,
- *	    %false if no vmap_area exists
- *
- * Find vmap_areas end addresses of which enclose @end.  ie. if not
- * NULL, *pnext->va_end > @end and *pprev->va_end <= @end.
+ * Returns: vmap_area if it is found. If there is no such area
+ *   the first highest(reverse order) vmap_area is returned
+ *   i.e. va->va_start < addr && va->va_end < addr or NULL
+ *   if there are no any areas before @addr.
  */
-static bool pvm_find_next_prev(unsigned long end,
-			       struct vmap_area **pnext,
-			       struct vmap_area **pprev)
+static struct vmap_area *
+pvm_find_va_enclose_addr(unsigned long addr)
 {
-	struct rb_node *n = vmap_area_root.rb_node;
-	struct vmap_area *va = NULL;
+	struct vmap_area *va, *tmp;
+	struct rb_node *n;
+
+	n = free_vmap_area_root.rb_node;
+	va = NULL;
 
 	while (n) {
-		va = rb_entry(n, struct vmap_area, rb_node);
-		if (end < va->va_end)
-			n = n->rb_left;
-		else if (end > va->va_end)
+		tmp = rb_entry(n, struct vmap_area, rb_node);
+		if (tmp->va_start <= addr) {
+			va = tmp;
+			if (tmp->va_end >= addr)
+				break;
+
 			n = n->rb_right;
-		else
-			break;
+		} else {
+			n = n->rb_left;
+		}
 	}
 
-	if (!va)
-		return false;
-
-	if (va->va_end > end) {
-		*pnext = va;
-		*pprev = node_to_va(rb_prev(&(*pnext)->rb_node));
-	} else {
-		*pprev = va;
-		*pnext = node_to_va(rb_next(&(*pprev)->rb_node));
-	}
-	return true;
+	return va;
 }
 
 /**
- * pvm_determine_end - find the highest aligned address between two vmap_areas
- * @pnext: in/out arg for the next vmap_area
- * @pprev: in/out arg for the previous vmap_area
- * @align: alignment
- *
- * Returns: determined end address
+ * pvm_determine_end_from_reverse - find the highest aligned address
+ * of free block below VMALLOC_END
+ * @va:
+ *   in - the VA we start the search(reverse order);
+ *   out - the VA with the highest aligned end address.
  *
- * Find the highest aligned address between *@pnext and *@pprev below
- * VMALLOC_END.  *@pnext and *@pprev are adjusted so that the aligned
- * down address is between the end addresses of the two vmap_areas.
- *
- * Please note that the address returned by this function may fall
- * inside *@pnext vmap_area.  The caller is responsible for checking
- * that.
+ * Returns: determined end address within vmap_area
  */
-static unsigned long pvm_determine_end(struct vmap_area **pnext,
-				       struct vmap_area **pprev,
-				       unsigned long align)
+static unsigned long
+pvm_determine_end_from_reverse(struct vmap_area **va, unsigned long align)
 {
-	const unsigned long vmalloc_end = VMALLOC_END & ~(align - 1);
+	unsigned long vmalloc_end = VMALLOC_END & ~(align - 1);
 	unsigned long addr;
 
-	if (*pnext)
-		addr = min((*pnext)->va_start & ~(align - 1), vmalloc_end);
-	else
-		addr = vmalloc_end;
-
-	while (*pprev && (*pprev)->va_end > addr) {
-		*pnext = *pprev;
-		*pprev = node_to_va(rb_prev(&(*pnext)->rb_node));
+	if (likely(*va)) {
+		list_for_each_entry_from_reverse((*va),
+				&free_vmap_area_list, list) {
+			addr = min((*va)->va_end & ~(align - 1), vmalloc_end);
+			if ((*va)->va_start < addr)
+				return addr;
+		}
 	}
 
-	return addr;
+	return 0;
 }
 
 /**
@@ -2496,12 +2979,12 @@ static unsigned long pvm_determine_end(struct vmap_area **pnext,
  * to gigabytes.  To avoid interacting with regular vmallocs, these
  * areas are allocated from top.
  *
- * Despite its complicated look, this allocator is rather simple.  It
- * does everything top-down and scans areas from the end looking for
- * matching slot.  While scanning, if any of the areas overlaps with
- * existing vmap_area, the base address is pulled down to fit the
- * area.  Scanning is repeated till all the areas fit and then all
- * necessary data structures are inserted and the result is returned.
+ * Despite its complicated look, this allocator is rather simple. It
+ * does everything top-down and scans free blocks from the end looking
+ * for matching base. While scanning, if any of the areas do not fit the
+ * base address is pulled down to fit the area. Scanning is repeated till
+ * all the areas fit and then all necessary data structures are inserted
+ * and the result is returned.
  */
 struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 				     const size_t *sizes, int nr_vms,
@@ -2509,11 +2992,12 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 {
 	const unsigned long vmalloc_start = ALIGN(VMALLOC_START, align);
 	const unsigned long vmalloc_end = VMALLOC_END & ~(align - 1);
-	struct vmap_area **vas, *prev, *next;
+	struct vmap_area **vas, *va;
 	struct vm_struct **vms;
 	int area, area2, last_area, term_area;
-	unsigned long base, start, end, last_end;
+	unsigned long base, start, size, end, last_end;
 	bool purged = false;
+	enum fit_type type;
 
 	/* verify parameters and allocate data structures */
 	BUG_ON(offset_in_page(align) || !is_power_of_2(align));
@@ -2549,7 +3033,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 		goto err_free2;
 
 	for (area = 0; area < nr_vms; area++) {
-		vas[area] = kzalloc(sizeof(struct vmap_area), GFP_KERNEL);
+		vas[area] = kmem_cache_zalloc(vmap_area_cachep, GFP_KERNEL);
 		vms[area] = kzalloc(sizeof(struct vm_struct), GFP_KERNEL);
 		if (!vas[area] || !vms[area])
 			goto err_free;
@@ -2562,49 +3046,29 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 	start = offsets[area];
 	end = start + sizes[area];
 
-	if (!pvm_find_next_prev(vmap_area_pcpu_hole, &next, &prev)) {
-		base = vmalloc_end - last_end;
-		goto found;
-	}
-	base = pvm_determine_end(&next, &prev, align) - end;
+	va = pvm_find_va_enclose_addr(vmalloc_end);
+	base = pvm_determine_end_from_reverse(&va, align) - end;
 
 	while (true) {
-		BUG_ON(next && next->va_end <= base + end);
-		BUG_ON(prev && prev->va_end > base + end);
-
 		/*
 		 * base might have underflowed, add last_end before
 		 * comparing.
 		 */
-		if (base + last_end < vmalloc_start + last_end) {
-			spin_unlock(&vmap_area_lock);
-			if (!purged) {
-				purge_vmap_area_lazy();
-				purged = true;
-				goto retry;
-			}
-			goto err_free;
-		}
+		if (base + last_end < vmalloc_start + last_end)
+			goto overflow;
 
 		/*
-		 * If next overlaps, move base downwards so that it's
-		 * right below next and then recheck.
+		 * Fitting base has not been found.
 		 */
-		if (next && next->va_start < base + end) {
-			base = pvm_determine_end(&next, &prev, align) - end;
-			term_area = area;
-			continue;
-		}
+		if (va == NULL)
+			goto overflow;
 
 		/*
-		 * If prev overlaps, shift down next and prev and move
-		 * base so that it's right below new next and then
-		 * recheck.
+		 * If this VA does not fit, move base downwards and recheck.
 		 */
-		if (prev && prev->va_end > base + start)  {
-			next = prev;
-			prev = node_to_va(rb_prev(&next->rb_node));
-			base = pvm_determine_end(&next, &prev, align) - end;
+		if (base + start < va->va_start || base + end > va->va_end) {
+			va = node_to_va(rb_prev(&va->rb_node));
+			base = pvm_determine_end_from_reverse(&va, align) - end;
 			term_area = area;
 			continue;
 		}
@@ -2616,21 +3080,40 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 		area = (area + nr_vms - 1) % nr_vms;
 		if (area == term_area)
 			break;
+
 		start = offsets[area];
 		end = start + sizes[area];
-		pvm_find_next_prev(base + end, &next, &prev);
+		va = pvm_find_va_enclose_addr(base + end);
 	}
-found:
+
 	/* we've found a fitting base, insert all va's */
 	for (area = 0; area < nr_vms; area++) {
-		struct vmap_area *va = vas[area];
+		int ret;
 
-		va->va_start = base + offsets[area];
-		va->va_end = va->va_start + sizes[area];
-		__insert_vmap_area(va);
-	}
+		start = base + offsets[area];
+		size = sizes[area];
 
-	vmap_area_pcpu_hole = base + offsets[last_area];
+		va = pvm_find_va_enclose_addr(start);
+		if (WARN_ON_ONCE(va == NULL))
+			/* It is a BUG(), but trigger recovery instead. */
+			goto recovery;
+
+		type = classify_va_fit_type(va, start, size);
+		if (WARN_ON_ONCE(type == NOTHING_FIT))
+			/* It is a BUG(), but trigger recovery instead. */
+			goto recovery;
+
+		ret = adjust_va_to_fit_type(va, start, size, type);
+		if (unlikely(ret))
+			goto recovery;
+
+		/* Allocated area. */
+		va = vas[area];
+		va->va_start = start;
+		va->va_end = start + size;
+
+		insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
+	}
 
 	spin_unlock(&vmap_area_lock);
 
@@ -2642,9 +3125,38 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 	kfree(vas);
 	return vms;
 
+recovery:
+	/* Remove previously inserted areas. */
+	while (area--) {
+		__free_vmap_area(vas[area]);
+		vas[area] = NULL;
+	}
+
+overflow:
+	spin_unlock(&vmap_area_lock);
+	if (!purged) {
+		purge_vmap_area_lazy();
+		purged = true;
+
+		/* Before "retry", check if we recover. */
+		for (area = 0; area < nr_vms; area++) {
+			if (vas[area])
+				continue;
+
+			vas[area] = kmem_cache_zalloc(
+				vmap_area_cachep, GFP_KERNEL);
+			if (!vas[area])
+				goto err_free;
+		}
+
+		goto retry;
+	}
+
 err_free:
 	for (area = 0; area < nr_vms; area++) {
-		kfree(vas[area]);
+		if (vas[area])
+			kmem_cache_free(vmap_area_cachep, vas[area]);
+
 		kfree(vms[area]);
 	}
 err_free2:
-- 
2.11.0