mm/hugetlb: retry to allocate for early boot hugepage allocation

mm/hugetlb: retry to allocate for early boot hugepage allocation

In cloud environments with massive hugepage reservations (95%+ of system
RAM), single-attempt allocation during early boot often fails due to
memory pressure.

Commit 91f386bf0772 ("hugetlb: batch freeing of vmemmap pages")
intensified this by deferring page frees, increase peak memory usage
during allocation.

Introduce a retry mechanism that leverages vmemmap optimization reclaim
(~1.6% memory) when available.  Upon initial allocation failure, the
system retries until successful or no further progress is made, ensuring
reliable hugepage allocation while preserving batched vmemmap freeing
benefits.

Testing on a 256G machine allocating 252G of hugepages:
Before: 128056/129024 hugepages allocated
After:  Successfully allocated all 129024 hugepages

Link: https://lkml.kernel.org/r/20250901082052.3247-1-lirongqing@baidu.com
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Li RongQing <lirongqing@baidu.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>