mm: remove migration for HugePage in isolate_single_pageblock()

The gigantic page size may larger than memory block size, so memory
offline always fails in this case after commit b2c9e2fb ("mm: make
alloc_contig_range work at pageblock granularity"),

offline_pages
  start_isolate_page_range
    start_isolate_page_range(isolate_before=true)
      isolate [isolate_start, isolate_start + pageblock_nr_pages)
    start_isolate_page_range(isolate_before=false)
      isolate [isolate_end - pageblock_nr_pages, isolate_end) pageblock
       	__alloc_contig_migrate_range
          isolate_migratepages_range
            isolate_migratepages_block
              isolate_or_dissolve_huge_page
                if (hstate_is_gigantic(h))
                    return -ENOMEM;

[   15.815756] memory offlining [mem 0x3c0000000-0x3c7ffffff] failed due to failure to isolate range

Gigantic PageHuge is bigger than a pageblock, but since it is freed as
order-0 pages, its pageblocks after being freed will get to the right
free list.  There is no need to have special handling code for them in
start_isolate_page_range().  For both alloc_contig_range() and memory
offline cases, the migration code after start_isolate_page_range() will
be able to migrate gigantic PageHuge when possible.  Let's clean up
start_isolate_page_range() and fix the aforementioned memory offline
failure issue all together.

Let's clean up start_isolate_page_range() and fix the aforementioned
memory offline failure issue all together.

Link: https://lkml.kernel.org/r/20240820032630.1894770-1-wangkefeng.wang@huawei.com


Fixes: b2c9e2fb ("mm: make alloc_contig_range work at pageblock granularity")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>