On Fri, May 27, 2016 at 09:39:53AM +0800, Qu Wenruo wrote:

Any comment?

This patch does not fix the submitted generic/352[1] and generic/353[2] 
test cases, but also introduce a much better structure and design for 
later backref walk use.

Instead of a list and do a O(n^3)~O(n^4) iteration for fiemap ioctl on a 
reflinked(deduped) file, it's now only O(n)~O(nlogn) for SHARED flag 
check to pass generic/352.

This is a good improvement, though there's potentially hidden cost in
the allocations and maintaining the temporary structures. Do you have
actual performance numbers?