Re: [PATCH v20 3/7 RESEND] xbitmap: add more operations

[Wei Wang]

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