On 12/21/2017 10:37 PM, Tetsuo Handa wrote:
Matthew Wilcox wrote:
+/**
+ * xb_find_set - find the next set bit in a range of bits
+ * @xb: the xbitmap to search from
+ * @offset: the offset in the range to start searching
+ * @size: the size of the range
+ *
+ * Returns: the found bit or, @size if no set bit is found.
+ */
+unsigned long xb_find_set(struct xb *xb, unsigned long size,
+ unsigned long offset)
+{
+ struct radix_tree_root *root = &xb->xbrt;
+ struct radix_tree_node *node;
+ void __rcu **slot;
+ struct ida_bitmap *bitmap;
+ unsigned long index = offset / IDA_BITMAP_BITS;
+ unsigned long index_end = size / IDA_BITMAP_BITS;
+ unsigned long bit = offset % IDA_BITMAP_BITS;
+
+ if (unlikely(offset >= size))
+ return size;
+
+ while (index <= index_end) {
+ unsigned long ret;
+ unsigned int nbits = size - index * IDA_BITMAP_BITS;
+
+ bitmap = __radix_tree_lookup(root, index, &node, &slot);
+
+ if (!node && !bitmap)
+ return size;
+
+ if (bitmap) {
+ if (nbits > IDA_BITMAP_BITS)
+ nbits = IDA_BITMAP_BITS;
+
+ ret = find_next_bit(bitmap->bitmap, nbits, bit);
+ if (ret != nbits)
+ return ret + index * IDA_BITMAP_BITS;
+ }
+ bit = 0;
+ index++;
+ }
+
+ return size;
+}
+EXPORT_SYMBOL(xb_find_set);
This is going to be slower than the implementation I sent yesterday. If I
call:
xb_init(xb);
xb_set_bit(xb, ULONG_MAX);
xb_find_set(xb, ULONG_MAX, 0);
it's going to call __radix_tree_lookup() 16 quadrillion times.
My implementation will walk the tree precisely once.
Yes. Wei's patch still can not work.
We should start reviewing Matthew's implementation.
It runs without any issue on my machine. I didn't generate an "xbitmap"
executable (I just found adding xbitmap executable causes a build error
due to a Makefile error), instead, I tested it within "main" and it
passed all the tests.
Matthew has implemented a new version, let's start from there.
Best,
Wei
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