init,mm: fold late call to page_ext_init() to page_alloc_init_late()

When deferred initialization of struct pages is enabled, page_ext_init()
must be called after all the deferred initialization is done, but there is
no point to keep it a separate call from kernel_init_freeable() right
after page_alloc_init_late().

Fold the call to page_ext_init() into page_alloc_init_late() and localize
deferred_struct_pages variable.

Link: https://lkml.kernel.org/r/20230321170513.2401534-11-rppt@kernel.org
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Doug Berger <opendmb@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/page_ext.h

@@ -29,8 +29,6 @@ struct page_ext_operations {
 	bool need_shared_flags;
 };
 
-extern bool deferred_struct_pages;
-
 #ifdef CONFIG_PAGE_EXTENSION
 
 /*