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Commit d5274261 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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[PATCH] radix tree: early termination of tag clearing 



Correctly determine the tags to be cleared in radix_tree_delete() so we
don't keep moving up the tree clearing tags that we don't need to.  For
example, if a tag is simply not set in the deleted item, nor anywhere up
the tree, radix_tree_delete() would attempt to clear it up the entire
height of the tree.

Also, tag_set() was made conditional so as not to dirty too many cachelines
high up in the radix tree.  Instead, put this logic into
radix_tree_tag_set().

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 6e954b9e

lib/radix-tree.c

+23 −17
Original line number Diff line number Diff line
@@ -137,18 +137,17 @@ int radix_tree_preload(gfp_t gfp_mask) 


static inline void tag_set(struct radix_tree_node *node, int tag, int offset)

{

	if (!test_bit(offset, &node->tags[tag][0]))

		__set_bit(offset, &node->tags[tag][0]);

	__set_bit(offset, node->tags[tag]);

}



static inline void tag_clear(struct radix_tree_node *node, int tag, int offset)

{

	__clear_bit(offset, &node->tags[tag][0]);

	__clear_bit(offset, node->tags[tag]);

}



static inline int tag_get(struct radix_tree_node *node, int tag, int offset)

{

	return test_bit(offset, &node->tags[tag][0]);

	return test_bit(offset, node->tags[tag]);

}



/*
@@ -375,6 +374,7 @@ void *radix_tree_tag_set(struct radix_tree_root *root, 
		int offset;



		offset = (index >> shift) & RADIX_TREE_MAP_MASK;

		if (!tag_get(slot, tag, offset))

			tag_set(slot, tag, offset);

		slot = slot->slots[offset];

		BUG_ON(slot == NULL);
@@ -435,6 +435,8 @@ void *radix_tree_tag_clear(struct radix_tree_root *root, 
		goto out;



	do {

		if (!tag_get(pathp->node, tag, pathp->offset))

			goto out;

		tag_clear(pathp->node, tag, pathp->offset);

		if (any_tag_set(pathp->node, tag))

			goto out;
@@ -695,6 +697,8 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index) 
	void *ret = NULL;

	char tags[RADIX_TREE_TAGS];

	int nr_cleared_tags;

	int tag;

	int offset;



	height = root->height;

	if (index > radix_tree_maxindex(height))
@@ -705,16 +709,14 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index) 
	slot = root->rnode;



	for ( ; height > 0; height--) {

		int offset;



		if (slot == NULL)

			goto out;



		pathp++;

		offset = (index >> shift) & RADIX_TREE_MAP_MASK;

		pathp[1].offset = offset;

		pathp[1].node = slot;

		pathp->offset = offset;

		pathp->node = slot;

		slot = slot->slots[offset];

		pathp++;

		shift -= RADIX_TREE_MAP_SHIFT;

	}
@@ -727,24 +729,28 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index) 
	/*

	 * Clear all tags associated with the just-deleted item

	 */

	memset(tags, 0, sizeof(tags));

	do {

		int tag;

	nr_cleared_tags = 0;

	for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {

		if (tag_get(pathp->node, tag, pathp->offset)) {

			tag_clear(pathp->node, tag, pathp->offset);

			tags[tag] = 0;

			nr_cleared_tags++;

		} else

			tags[tag] = 1;

	}



		nr_cleared_tags = RADIX_TREE_TAGS;

	for (pathp--; nr_cleared_tags && pathp->node; pathp--) {

		for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {

			if (tags[tag])

				continue;



			tag_clear(pathp->node, tag, pathp->offset);



			if (any_tag_set(pathp->node, tag)) {

				tags[tag] = 1;

				nr_cleared_tags--;

			}

		}

		pathp--;

	} while (pathp->node && nr_cleared_tags);

	}



	/* Now free the nodes we do not need anymore */

	for (pathp = orig_pathp; pathp->node; pathp--) {