FAILED: patch "[PATCH] mm/hugetlb_cma: round up per_node before logging it" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] mm/hugetlb_cma: round up per_node before logging it" failed to apply to 5.15-stable tree

[gregkh]

The patch below does not apply to the 5.15-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 <stable@vger.kernel.org>.

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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 8f5ce56b76303c55b78a87af996e2e0f8535f979
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026051242-tanned-unlatch-32ed@gregkh' --subject-prefix 'PATCH 5.15.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 <ekffu200098@gmail.com>
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

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>

diff --git a/mm/hugetlb_cma.c b/mm/hugetlb_cma.c
index f83ae4998990..7693ccefd0c6 100644
--- a/mm/hugetlb_cma.c
+++ b/mm/hugetlb_cma.c
@@ -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);
 	}

[PATCH 5.15.y] mm/hugetlb_cma: round up per_node before logging it

[Sasha Levin]

From: Sang-Heon Jeon <ekffu200098@gmail.com>

[ 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

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>
[ applied the one-line `round_up` to `mm/hugetlb.c` ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/hugetlb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 64dfa3fcd554b..8b4bc38e1c0a6 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6493,6 +6493,7 @@ 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