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/*
* 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;
}
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