Struct page cleanup

For the first three tabs, each row represents four bytes. The first row (or two rows for the 64-bit struct page) are 'flags', and each cell represents one bit with a two-letter abbreviation of the name of the flag.
Then there's a row of headers which enumerate some of the users of struct page (page cache, anon, slab, slub, page tables, etc)
At this point the meaning of each cell changes; one cell represents one byte.
The dark lines represent boundaries within the struct page, eg we currently have:

struct page {
union {
struct address_space *mapping;
/* deferred_list.head */
};
union {
unsigned long index;
/* deferred_list.tail */
};
...
};

so there's a dark line between mapping and index to show that we can't just put a list_head into the union.

Fields which have the same meaning between all page types are shown without vertical lines (eg refcount) while fields which happen to be used for the same meaning between different page types are shown with vertical lines.

Hope that's helpful. Yes, it's a confusing diagram. I spent hours trying to come up with a good graphical representation of what's going on in struct page, and this was the best I could do.