Kfsio library: implement IOBuffer::CopyIn method with position between "used"/"consumed" and available space, to avoid searching for the boundary, by traversing the scatter-gatherer buffers linked list..
Client library: use IOBuffer::CopyIn() method with position argument, in order to get rid of O^2 linked list traversal. The traversal is a major cpu hog with chunk server where io buffer size is 4K and typical recovery size is 1MB, or 256 buffers / linked list entries.