Requesting clarification on Vacuuming/Freezing behaviour

Hi,
I got some time to relook at the index with the snapshot patch. Still i
need to complete the freezing of index tuples with the snapshot.
a) When i was looking at the code for freezing heap tuples, i found out the
following. While freezing we log the complete block(not just the tuples we
froze).
b) Again after removing the dead tuples and fragmentation, we log the
complete block.

As i understand, Vacuum is one atomic operation. Why do we need to make this
extra protection for Freezing?
I think the fix should be very simple. Before logging the Frozen block, we
need to check whether there are any dead tuples removed from it..

Please clarify on whether i am missing something important..

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Thanks,
Gokul.
CertoSQL Project,
Allied Solution Group.
(www.alliedgroups.com)