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radix-tree: add radix_tree_prev_hole()

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The counterpart of radix_tree_next_hole(). To be used by context readahead.

Signed-off-by: Wu Fengguang <[email protected]>
Cc: Vladislav Bolkhovitin <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Jeff Moyer <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Ying Han <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Wu Fengguang 2009-06-16 15:31:32 -07:00 • committed by Linus Torvalds
commit dc566127dd
2 changed files with 39 additions and 0 deletions
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37
lib/radix-tree.c
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@ -666,6 +666,43 @@ unsigned long radix_tree_next_hole(struct radix_tree_root *root,
}
EXPORT_SYMBOL(radix_tree_next_hole);
/**
* radix_tree_prev_hole - find the prev hole (not-present entry)
* @root: tree root
* @index: index key
* @max_scan: maximum range to search
*
* Search backwards in the range [max(index-max_scan+1, 0), index]
* for the first hole.
*
* Returns: the index of the hole if found, otherwise returns an index
* outside of the set specified (in which case 'index - return >= max_scan'
* will be true). In rare cases of wrap-around, LONG_MAX will be returned.
*
* radix_tree_next_hole may be called under rcu_read_lock. However, like
* radix_tree_gang_lookup, this will not atomically search a snapshot of
* the tree at a single point in time. For example, if a hole is created
* at index 10, then subsequently a hole is created at index 5,
* radix_tree_prev_hole covering both indexes may return 5 if called under
* rcu_read_lock.
*/
unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
unsigned long index, unsigned long max_scan)
{
unsigned long i;
for (i = 0; i < max_scan; i++) {
if (!radix_tree_lookup(root, index))
break;
index--;
if (index == LONG_MAX)
break;
}
return index;
}
EXPORT_SYMBOL(radix_tree_prev_hole);
static unsigned int
__lookup(struct radix_tree_node *slot, void ***results, unsigned long index,
unsigned int max_items, unsigned long *next_index)