[PATCHv4 4/7] mm: pack compound_dtor and compound_order into one word in struct page

The patch halves space occupied by compound_dtor and compound_order in struct page. For compound_order, it's trivial long -> short conversion. For get_compound_page_dtor(), we now use hardcoded table for destructor lookup and store its index in the struct page instead of direct pointer to

[PATCHv4 4/7] mm: pack compound_dtor and compound_order into one word in struct page

The patch halves space occupied by compound_dtor and compound_order in struct page. For compound_order, it's trivial long - short conversion. For get_compound_page_dtor(), we now use hardcoded table for destructor lookup and store its index in the struct page instead of direct pointer to