s390/mm: Get total ram pages from memblock

On s390, zero page's size relies on total ram pages.

Since we plan to move the accounting into __free_pages_core(),
totalram_pages may not represent the total usable pages on system
at this point when defer_init is enabled.

We can get the total usable pages from memblock directly. The size maybe
not accurate due to the alignment, but enough for the calculation.

Signed-off-by: Wei Yang <[e-mail]>
CC: Mike Rapoport (IBM) <[e-mail]>
CC: David Hildenbrand <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vasily Gorbik <[e-mail]>
Signed-off-by: Alexander Gordeev <[e-mail]>

arch/s390/mm/init.c

···
 
 static void __init setup_zero_pages(void)
 {
+	unsigned long total_pages = PHYS_PFN(memblock_phys_mem_size() - memblock_reserved_size());
 	unsigned int order;
 	struct page *page;
 	int i;
···
 	order = 7;
 
 	/* Limit number of empty zero pages for small memory sizes */
-	while (order > 2 && (totalram_pages() >> 10) < (1UL << order))
+	while (order > 2 && (total_pages >> 10) < (1UL << order))
 		order--;
 
 	empty_zero_page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);