mm/migrate: fix NR_ISOLATED corruption on 64-bit

Similar to commit 2da9f630 ("mm/vmscan: fix NR_ISOLATED_FILE
corruption on 64-bit") avoid using unsigned int for nr_pages.  With
unsigned int type the large unsigned int converts to a large positive
signed long.

Symptoms include CMA allocations hanging forever due to
alloc_contig_range->...->isolate_migratepages_block waiting forever in
"while (unlikely(too_many_isolated(pgdat)))".

Link: https://lkml.kernel.org/r/20210728042531.359409-1-aneesh.kumar@linux.ibm.com
Fixes: c5fc5c3a ("mm: migrate: account THP NUMA migration counters correctly")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/migrate.c

@@ -2068,7 +2068,7 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
 	LIST_HEAD(migratepages);
 	new_page_t *new;
 	bool compound;
-	unsigned int nr_pages = thp_nr_pages(page);
+	int nr_pages = thp_nr_pages(page);
 
 	/*
 	 * PTE mapped THP or HugeTLB page can't reach here so the page could