prio_tree: remove

After both prio_tree users have been converted to use red-black trees,
there is no need to keep around the prio tree library anymore.

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 0 insertions, 109 deletions

diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX
index 49c051380daf..f54273e2ac97 100644
--- a/Documentation/00-INDEX
+++ b/Documentation/00-INDEX
@@ -270,8 +270,6 @@ preempt-locking.txt
         - info on locking under a preemptive kernel.
 printk-formats.txt
         - how to get printk format specifiers right
-prio_tree.txt
-        - info on radix-priority-search-tree use for indexing vmas.
 ramoops.txt
         - documentation of the ramoops oops/panic logging module.
 rbtree.txt
diff --git a/Documentation/prio_tree.txt b/Documentation/prio_tree.txt
deleted file mode 100644
index 3aa68f9a117b..000000000000
--- a/Documentation/prio_tree.txt
+++ /dev/null
@@ -1,107 +0,0 @@
-The prio_tree.c code indexes vmas using 3 different indexes:
-        * heap_index  = vm_pgoff + vm_size_in_pages : end_vm_pgoff
-        * radix_index = vm_pgoff : start_vm_pgoff
-        * size_index = vm_size_in_pages
-
-A regular radix-priority-search-tree indexes vmas using only heap_index and
-radix_index. The conditions for indexing are:
-        * ->heap_index >= ->left->heap_index &&
-                ->heap_index >= ->right->heap_index
-        * if (->heap_index == ->left->heap_index)
-                then ->radix_index < ->left->radix_index;
-        * if (->heap_index == ->right->heap_index)
-                then ->radix_index < ->right->radix_index;
-        * nodes are hashed to left or right subtree using radix_index
-          similar to a pure binary radix tree.
-
-A regular radix-priority-search-tree helps to store and query
-intervals (vmas). However, a regular radix-priority-search-tree is only
-suitable for storing vmas with different radix indices (vm_pgoff).
-
-Therefore, the prio_tree.c extends the regular radix-priority-search-tree
-to handle many vmas with the same vm_pgoff. Such vmas are handled in
-2 different ways: 1) All vmas with the same radix _and_ heap indices are
-linked using vm_set.list, 2) if there are many vmas with the same radix
-index, but different heap indices and if the regular radix-priority-search
-tree cannot index them all, we build an overflow-sub-tree that indexes such
-vmas using heap and size indices instead of heap and radix indices. For
-example, in the figure below some vmas with vm_pgoff = 0 (zero) are
-indexed by regular radix-priority-search-tree whereas others are pushed
-into an overflow-subtree. Note that all vmas in an overflow-sub-tree have
-the same vm_pgoff (radix_index) and if necessary we build different
-overflow-sub-trees to handle each possible radix_index. For example,
-in figure we have 3 overflow-sub-trees corresponding to radix indices
-0, 2, and 4.
-
-In the final tree the first few (prio_tree_root->index_bits) levels
-are indexed using heap and radix indices whereas the overflow-sub-trees below
-those levels (i.e. levels prio_tree_root->index_bits + 1 and higher) are
-indexed using heap and size indices. In overflow-sub-trees the size_index
-is used for hashing the nodes to appropriate places.
-
-Now, an example prio_tree:
-
-  vmas are represented [radix_index, size_index, heap_index]
-                 i.e., [start_vm_pgoff, vm_size_in_pages, end_vm_pgoff]
-
-level  prio_tree_root->index_bits = 3
------
-                                                                                                _
-  0                                                     [0,7,7]                                  |
-                                                        /     \                                  |
-                                      ------------------       ------------                      |     Regular
-                                     /                                     \                     |  radix priority
-  1                             [1,6,7]                                   [4,3,7]                |   search tree
-                                /     \                                   /     \                |
-                         -------       -----                        ------       -----           |  heap-and-radix
-                        /                   \                      /                  \          |      indexed
-  2                 [0,6,6]                [2,5,7]              [5,2,7]             [6,1,7]      |
-                    /     \                /     \              /     \             /     \      |
-  3             [0,5,5] [1,5,6]         [2,4,6] [3,4,7]     [4,2,6] [5,1,6]     [6,0,6] [7,0,7]  |
-                   /                       /                   /                                _
-                  /                       /                   /                                 _
-  4           [0,4,4]                 [2,3,5]              [4,1,5]                               |
-                 /                       /                    /                                  |
-  5          [0,3,3]                 [2,2,4]              [4,0,4]                                |  Overflow-sub-trees
-                /                       /                                                        |
-  6         [0,2,2]                 [2,1,3]                                                      |    heap-and-size
-               /                       /                                                         |       indexed
-  7        [0,1,1]                 [2,0,2]                                                       |
-              /                                                                                  |
-  8       [0,0,0]                                                                                |
-                                                                                                _
-
-Note that we use prio_tree_root->index_bits to optimize the height
-of the heap-and-radix indexed tree. Since prio_tree_root->index_bits is
-set according to the maximum end_vm_pgoff mapped, we are sure that all
-bits (in vm_pgoff) above prio_tree_root->index_bits are 0 (zero). Therefore,
-we only use the first prio_tree_root->index_bits as radix_index.
-Whenever index_bits is increased in prio_tree_expand, we shuffle the tree
-to make sure that the first prio_tree_root->index_bits levels of the tree
-is indexed properly using heap and radix indices.
-
-We do not optimize the height of overflow-sub-trees using index_bits.
-The reason is: there can be many such overflow-sub-trees and all of
-them have to be suffled whenever the index_bits increases. This may involve
-walking the whole prio_tree in prio_tree_insert->prio_tree_expand code
-path which is not desirable. Hence, we do not optimize the height of the
-heap-and-size indexed overflow-sub-trees using prio_tree->index_bits.
-Instead the overflow sub-trees are indexed using full BITS_PER_LONG bits
-of size_index. This may lead to skewed sub-trees because most of the
-higher significant bits of the size_index are likely to be 0 (zero). In
-the example above, all 3 overflow-sub-trees are skewed. This may marginally
-affect the performance. However, processes rarely map many vmas with the
-same start_vm_pgoff but different end_vm_pgoffs. Therefore, we normally
-do not require overflow-sub-trees to index all vmas.
-
-From the above discussion it is clear that the maximum height of
-a prio_tree can be prio_tree_root->index_bits + BITS_PER_LONG.
-However, in most of the common cases we do not need overflow-sub-trees,
-so the tree height in the common cases will be prio_tree_root->index_bits.
-
-It is fair to mention here that the prio_tree_root->index_bits
-is increased on demand, however, the index_bits is not decreased when
-vmas are removed from the prio_tree. That's tricky to do. Hence, it's
-left as a home work problem.
-
-