Duy Nguyen [off-list ref] wrote:

struct revindex_entry {
        off_t offset;
        unsigned int nr;
};

We need on entry per object, so 6.5M objects * 16 bytes = 104 MB. If
we break this struct apart and store two arrays of offset and nr in
struct packed_git, we save 4 bytes per struct, 26 MB total.

Can the offset array can be a union which stores
int32_t/uint32_t instead of off_t for projects which never
exceed 2/4GB?

Likewise, places object_entry where "unsigned long" and off_t
are 64-bit could benefit from being 32-bit.  Testing/maintenance
overhead could be bad, for those, though.