mm/hugetlb_cma: round up per_node before logging it

mm/hugetlb_cma: round up per_node before logging it

When the user requests a total hugetlb CMA size without per-node
specification, hugetlb_cma_reserve() computes per_node from
hugetlb_cma_size and the number of nodes that have memory

        per_node = DIV_ROUND_UP(hugetlb_cma_size,
                                nodes_weight(hugetlb_bootmem_nodes));

The reservation loop later computes

        size = round_up(min(per_node, hugetlb_cma_size - reserved),
                          PAGE_SIZE << order);

So the actually reserved per_node size is multiple of (PAGE_SIZE <<
order), but the logged per_node is not rounded up, so it may be smaller
than the actual reserved size.

For example, as the existing comment describes, if a 3 GB area is
requested on a machine with 4 NUMA nodes that have memory, 1 GB is
allocated on the first three nodes, but the printed log is

        hugetlb_cma: reserve 3072 MiB, up to 768 MiB per node

Round per_node up to (PAGE_SIZE << order) before logging so that the
printed log always matches the actual reserved size.  No functional change
to the actual reservation size, as the following case analysis shows

1. remaining (hugetlb_cma_size - reserved) >= rounded per_node
 - AS-IS: min() picks unrounded per_node;
    round_up() returns rounded per_node
 - TO-BE: min() picks rounded per_node;
    round_up() returns rounded per_node (no-op)
2. remaining < unrounded per_node
 - AS-IS: min() picks remaining;
    round_up() returns round_up(remaining)
 - TO-BE: min() picks remaining;
    round_up() returns round_up(remaining)
3. unrounded per_node <= remaining < rounded per_node
 - AS-IS: min() picks unrounded per_node;
    round_up() returns rounded per_node
 - TO-BE: min() picks remaining;
    round_up() returns round_up(remaining) equals rounded per_node

Link: https://lore.kernel.org/20260422143353.852257-1-ekffu200098@gmail.com
Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma") # 5.7
Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>