FAILED: patch "[PATCH] mm/hugetlb_cma: round up per_node before logging it" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 8f5ce56b76303c55b78a87af996e2e0f8535f979
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026051241-flakily-uniquely-50ca@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 8f5ce56b76303c55b78a87af996e2e0f8535f979 Mon Sep 17 00:00:00 2001
From: Sang-Heon Jeon <[email protected]>
Date: Wed, 22 Apr 2026 23:33:53 +0900
Subject: [PATCH] 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

index f83ae4998990..7693ccefd0c6 100644
@@ -204,6 +204,7 @@ void __init hugetlb_cma_reserve(void)
 		 */
 		per_node = DIV_ROUND_UP(hugetlb_cma_size,
 					nodes_weight(hugetlb_bootmem_nodes));
+		per_node = round_up(per_node, PAGE_SIZE << order);
 		pr_info("hugetlb_cma: reserve %lu MiB, up to %lu MiB per node\n",
 			hugetlb_cma_size / SZ_1M, per_node / SZ_1M);
 	}

From: Sang-Heon Jeon <[email protected]>

[ Upstream commit 8f5ce56b76303c55b78a87af996e2e0f8535f979 ]

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

---
 mm/hugetlb.c | 1 +
 1 file changed, 1 insertion(+)

index aa0ef3bc4dd65..6a1e0eefd2540 100644
@@ -7493,6 +7493,7 @@ void __init hugetlb_cma_reserve(int order)
 		 * let's allocate 1 GB on first three nodes and ignore the last one.
 		 */
 		per_node = DIV_ROUND_UP(hugetlb_cma_size, nr_online_nodes);
+		per_node = round_up(per_node, PAGE_SIZE << order);
 		pr_info("hugetlb_cma: reserve %lu MiB, up to %lu MiB per node\n",
 			hugetlb_cma_size / SZ_1M, per_node / SZ_1M);
 	}

2.53.0