On 5/21/25 11:04 AM, Kuan-Wei Chiu wrote:
Hi Matthew,
Recently noticed that the current heapify method in min_heap.h may
degrade performance when the heap contains many compare-equal elements,
compared to the previous version.
In detail, the new heapify reduces the number of comparisons by about
50% when all elements are distinct. However, when all elements are
equal, the comparison count can degrade from O(1) to O(log n).
I don't have enough domain knowledge of dm-vdo, so I'd like to ask
whether it uses heaps with many compare-equal elements. If so, I'll
work on fixing the issue.
Regards,
Kuan-Wei
Hi Kuan-Wei,
dm-vdo uses heapify for two different operations, but in both cases we
define heap elements that can never be equal to each other. So I think
this is not an issue for dm-vdo. (We have not noticed any issues with
this in our regular testing, either.)
Matt
