Jeff King <peff@xxxxxxxx> writes: > I also wondered why other versions do not have a similar problem. After > all, cache entries contain pathnames which are going to be of varying > lengths. But this seems telling: > > $ git grep -m1 -B1 -A2 align_padding_size > read-cache.c-/* These are only used for v3 or lower */ > read-cache.c:#define align_padding_size(size, len) ((size + (len) + 8) & ~7) - (size + len) > read-cache.c-#define align_flex_name(STRUCT,len) ((offsetof(struct STRUCT,data) + (len) + 8) & ~7) > read-cache.c-#define ondisk_cache_entry_size(len) align_flex_name(ondisk_cache_entry,len) > > So we actually pad the entries in earlier versions to align them, but > don't in v4. I'm not sure if that was a conscious choice to save space, > or an unintended consequence (though it is mentioned in the docs, I > think that came after the code). I think we didn't even have on-disk vs in-core distinction in the early index code. The active_cache[] array used to be an array of pointers into the (read-only) mmapped memory, peeking into on-disk index we just "read". Back when v4 was introduced, that arrangement was (thought to be) long gone---we iterated over the mmapped memory and used create_from_disk() to munge the on-disk representation into a machine native form. At that point, there was no point in having the padding---we are supposed to be using get_beXX() and stuff without having to worry about alignment requirements.
