/*
   * mm/prio_tree.c - priority search tree for mapping->i_mmap
   *
   * Copyright (C) 2004, Rajesh Venkatasubramanian <vrajesh@umich.edu>
   *
   * This file is released under the GPL v2.
   *
   * Based on the radix priority search tree proposed by Edward M. McCreight
   * SIAM Journal of Computing, vol. 14, no.2, pages 257-276, May 1985
   *
   * 02Feb2004	Initial version
   */
  
  #include <linux/mm.h>
  #include <linux/prio_tree.h>

  #include <linux/prefetch.h>

  
  /*
   * See lib/prio_tree.c for details on the general radix priority search tree
   * code.
   */
  
  /*
   * The following #defines are mirrored from lib/prio_tree.c. They're only used
   * for debugging, and should be removed (along with the debugging code using
   * them) when switching also VMAs to the regular prio_tree code.
   */
  
  #define RADIX_INDEX(vma)  ((vma)->vm_pgoff)
  #define VMA_SIZE(vma)	  (((vma)->vm_end - (vma)->vm_start) >> PAGE_SHIFT)
  /* avoid overflow */
  #define HEAP_INDEX(vma)   ((vma)->vm_pgoff + (VMA_SIZE(vma) - 1))
  
  /*
   * Radix priority search tree for address_space->i_mmap
   *
   * For each vma that map a unique set of file pages i.e., unique [radix_index,

   * heap_index] value, we have a corresponding priority search tree node. If

   * multiple vmas have identical [radix_index, heap_index] value, then one of
   * them is used as a tree node and others are stored in a vm_set list. The tree
   * node points to the first vma (head) of the list using vm_set.head.
   *
   * prio_tree_root
   *      |
   *      A       vm_set.head
   *     / \      /
   *    L   R -> H-I-J-K-M-N-O-P-Q-S
   *    ^   ^    <-- vm_set.list -->
   *  tree nodes
   *
   * We need some way to identify whether a vma is a tree node, head of a vm_set
   * list, or just a member of a vm_set list. We cannot use vm_flags to store
   * such information. The reason is, in the above figure, it is possible that
   * vm_flags' of R and H are covered by the different mmap_sems. When R is
   * removed under R->mmap_sem, H replaces R as a tree node. Since we do not hold
   * H->mmap_sem, we cannot use H->vm_flags for marking that H is a tree node now.
   * That's why some trick involving shared.vm_set.parent is used for identifying
   * tree nodes and list head nodes.
   *
   * vma radix priority search tree node rules:
   *
   * vma->shared.vm_set.parent != NULL    ==> a tree node
   *      vma->shared.vm_set.head != NULL ==> list of others mapping same range
   *      vma->shared.vm_set.head == NULL ==> no others map the same range
   *
   * vma->shared.vm_set.parent == NULL
   * 	vma->shared.vm_set.head != NULL ==> list head of vmas mapping same range
   * 	vma->shared.vm_set.head == NULL ==> a list node
   */
  
  /*
   * Add a new vma known to map the same set of pages as the old vma:
   * useful for fork's dup_mmap as well as vma_prio_tree_insert below.
   * Note that it just happens to work correctly on i_mmap_nonlinear too.
   */
  void vma_prio_tree_add(struct vm_area_struct *vma, struct vm_area_struct *old)
  {
  	/* Leave these BUG_ONs till prio_tree patch stabilizes */
  	BUG_ON(RADIX_INDEX(vma) != RADIX_INDEX(old));
  	BUG_ON(HEAP_INDEX(vma) != HEAP_INDEX(old));
  
  	vma->shared.vm_set.head = NULL;
  	vma->shared.vm_set.parent = NULL;
  
  	if (!old->shared.vm_set.parent)
  		list_add(&vma->shared.vm_set.list,
  				&old->shared.vm_set.list);
  	else if (old->shared.vm_set.head)
  		list_add_tail(&vma->shared.vm_set.list,
  				&old->shared.vm_set.head->shared.vm_set.list);
  	else {
  		INIT_LIST_HEAD(&vma->shared.vm_set.list);
  		vma->shared.vm_set.head = old;
  		old->shared.vm_set.head = vma;
  	}
  }
  
  void vma_prio_tree_insert(struct vm_area_struct *vma,
  			  struct prio_tree_root *root)
  {
  	struct prio_tree_node *ptr;
  	struct vm_area_struct *old;
  
  	vma->shared.vm_set.head = NULL;
  
  	ptr = raw_prio_tree_insert(root, &vma->shared.prio_tree_node);
  	if (ptr != (struct prio_tree_node *) &vma->shared.prio_tree_node) {
  		old = prio_tree_entry(ptr, struct vm_area_struct,
  					shared.prio_tree_node);
  		vma_prio_tree_add(vma, old);
  	}
  }
  
  void vma_prio_tree_remove(struct vm_area_struct *vma,
  			  struct prio_tree_root *root)
  {
  	struct vm_area_struct *node, *head, *new_head;
  
  	if (!vma->shared.vm_set.head) {
  		if (!vma->shared.vm_set.parent)
  			list_del_init(&vma->shared.vm_set.list);
  		else
  			raw_prio_tree_remove(root, &vma->shared.prio_tree_node);
  	} else {
  		/* Leave this BUG_ON till prio_tree patch stabilizes */
  		BUG_ON(vma->shared.vm_set.head->shared.vm_set.head != vma);
  		if (vma->shared.vm_set.parent) {
  			head = vma->shared.vm_set.head;
  			if (!list_empty(&head->shared.vm_set.list)) {
  				new_head = list_entry(
  					head->shared.vm_set.list.next,
  					struct vm_area_struct,
  					shared.vm_set.list);
  				list_del_init(&head->shared.vm_set.list);
  			} else
  				new_head = NULL;
  
  			raw_prio_tree_replace(root, &vma->shared.prio_tree_node,
  					&head->shared.prio_tree_node);
  			head->shared.vm_set.head = new_head;
  			if (new_head)
  				new_head->shared.vm_set.head = head;
  
  		} else {
  			node = vma->shared.vm_set.head;
  			if (!list_empty(&vma->shared.vm_set.list)) {
  				new_head = list_entry(
  					vma->shared.vm_set.list.next,
  					struct vm_area_struct,
  					shared.vm_set.list);
  				list_del_init(&vma->shared.vm_set.list);
  				node->shared.vm_set.head = new_head;
  				new_head->shared.vm_set.head = node;
  			} else
  				node->shared.vm_set.head = NULL;
  		}
  	}
  }
  
  /*
   * Helper function to enumerate vmas that map a given file page or a set of
   * contiguous file pages. The function returns vmas that at least map a single
   * page in the given range of contiguous file pages.
   */
  struct vm_area_struct *vma_prio_tree_next(struct vm_area_struct *vma,
  					struct prio_tree_iter *iter)
  {
  	struct prio_tree_node *ptr;
  	struct vm_area_struct *next;
  
  	if (!vma) {
  		/*
  		 * First call is with NULL vma
  		 */
  		ptr = prio_tree_next(iter);
  		if (ptr) {
  			next = prio_tree_entry(ptr, struct vm_area_struct,
  						shared.prio_tree_node);
  			prefetch(next->shared.vm_set.head);
  			return next;
  		} else
  			return NULL;
  	}
  
  	if (vma->shared.vm_set.parent) {
  		if (vma->shared.vm_set.head) {
  			next = vma->shared.vm_set.head;
  			prefetch(next->shared.vm_set.list.next);
  			return next;
  		}
  	} else {
  		next = list_entry(vma->shared.vm_set.list.next,
  				struct vm_area_struct, shared.vm_set.list);
  		if (!next->shared.vm_set.head) {
  			prefetch(next->shared.vm_set.list.next);
  			return next;
  		}
  	}
  
  	ptr = prio_tree_next(iter);
  	if (ptr) {
  		next = prio_tree_entry(ptr, struct vm_area_struct,
  					shared.prio_tree_node);
  		prefetch(next->shared.vm_set.head);
  		return next;
  	} else
  		return NULL;
  }