[..]
> > > What would actually be safer is to make the two subtypes explicit, and
> > > not have unused/ambiguous/overloaded members at all:
> > >
> > > struct zswap_entry {
> > > unsigned int length;
> > > struct obj_cgroup *objcg;
> > > };
> > >
> > > struct zswap_compressed_entry {
> > > struct zswap_entry entry;
> > > struct zswap_pool *pool;
> > > unsigned long handle;
> > > struct list_head lru;
> > > swp_entry_t swpentry;
> > > };
> > >
> > > struct zswap_samefilled_entry {
> > > struct zswap_entry entry;
> > > unsigned long value;
> > > };
> >
> > I think the 3 struct with embedded and container of is a bit complex,
> > because the state breaks into different struct members
>
> That's kind of the point. They're different types that have their own
> rules and code paths. The code as it is right now makes it seem like
> they're almost the same. From the above you can see that they have
> actually almost nothing in common (the bits in struct zswap_entry).
>
> This would force the code to show the difference as well.
>
> Depending on how Yosry's patches work out, this may or may not be
> worth doing. It's just an idea that could help make it easier.
I initially wanted to do something similar to splitting the structs
before not allocating an entry at all for same-filled pages, but I
ended up dropping it as the direct conversion was simple enough.
Anyway, I will post the patches some time next week (or today if I can
get around to test them). The discussion should be easier with code.
