Cracks and white stuff in loft

I've noticed a couple of things in our loft and I'm not sure whether or not they're serious or OK, so I'll list the things below and hopefully get some advice. Some background on the house - It's a late 1950s / early 1960s semi detached in Manchester, UK. The previous owner hadn't done much to it but I think had looked after it, though it had no gas central heating when we bought it and we're in the process of renovating. The loft was already boarded out.

Firstly, one of the rafters has a lot of white stuff on it - I'm not sure if this is dry rot - it looks like it has maybe been damp in the past, but I'm not sure if it's something that needs treating or it's just stained. I don't think it's getting damp now:

There's also a couple of small white blobs in other places which I'm wondering if they're also dry rot, or maybe just spider egg sacs:

There are a couple of cracks, the main one being in one of the beams that is about half way up the rafters:
and also one of the rafters has splintered:
I'm wondering if the splintering is maybe from it getting really hot up there and the wood expanding / contracting? I checked the insulation and most of it is pulled back a bit from the edges, so hopefully there's enough ventilation (there's maybe a couple of places where it's close to the roof, but mostly there's a gap:

So is there anything there that I should be concerned about?
Thanks

Almost certainly nothing to worry about.
It's not usual to find dry rot in a roof unless it has in some way been totally sealed; most roofs are draughty, which is fine.
The cracks (aka 'shakes') are nothing important either.
Looking at your pics, the roof looks clean and in good condition.

OK thanks, that's good to know. Puts my mind at ease
Cheers.

The white marks are from condensation on the felt in the loft, so check that the insulation isn't blocking the airflow. The white blobs are most likely spider sacs, but certainly not rot of any sort.