The notion of checkpoint size has come up in a few conversations in disagg. The first is the idea of file size – the block manager includes an API for getting the size of the file, but the disaggregated block manager doesn't deal with files. The "cleanest" analogue would seem to be the size of the checkpoint, but we'd have to get this from SLS.

Another place this is useful is when packing checkpoint address cookies. The checkpoint structure contains a size, which isn't useful in disagg so we just put the page ID. If we can easily get the checkpoint size, it would be nice to populate this field correctly. On the other hand, if we don't need it, we should leave it blank instead of putting something weird (the page ID) in it.