From: Sang-Heon Jeon Date: Fri, 17 Apr 2026 13:58:05 +0000 (+0900) Subject: mm/fake-numa: fix under-allocation detection in uniform split X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=3a3fc1dfd6a958615ebaab8fb251e89fc2b3f2f2;p=thirdparty%2Fkernel%2Flinux.git mm/fake-numa: fix under-allocation detection in uniform split When splitting NUMA node uniformly, split_nodes_size_interleave_uniform() returns the next absolute node ID, not the number of nodes created. The existing under-allocation detection logic compares next absolute node ID (ret) and request count (n), which only works when nid starts at 0. For example, on a system with 2 physical NUMA nodes (node 0: 2GB, node 1: 128MB) and numa=fake=8U, 8 fake nodes are successfully created from node 0 and split_nodes_size_interleave_uniform() returns 8. For node 1, fake node nid starts at 8, but only 4 fake nodes are created due to current FAKE_NODE_MIN_SIZE being 32MB, and split_nodes_size_interleave_uniform() returns 12. By existing under-allocation detection logic, "ret < n" (12 < 8) is false, so the under-allocation will not be detected. Fix under-allocation detection logic to compare the number of actually created nodes (ret - nid) against the request count (n). Also skip under-allocation detection logic for memoryless physical nodes where no fake nodes are created. Also, fix the outdated comment describing split_nodes_size_interleave_uniform() to match the actual return value. Signed-off-by: Sang-Heon Jeon Reported-by: Donghyeon Lee Reported-by: Munhui Chae Fixes: cc9aec03e58f ("x86/numa_emulation: Introduce uniform split capability") # 4.19 Link: https://patch.msgid.link/20260417135805.1758378-1-ekffu200098@gmail.com Signed-off-by: Mike Rapoport (Microsoft) --- diff --git a/mm/numa_emulation.c b/mm/numa_emulation.c index 703c8fa050480..55f26b22bb0be 100644 --- a/mm/numa_emulation.c +++ b/mm/numa_emulation.c @@ -214,7 +214,7 @@ static u64 uniform_size(u64 max_addr, u64 base, u64 hole, int nr_nodes) * Sets up fake nodes of `size' interleaved over physical nodes ranging from * `addr' to `max_addr'. * - * Returns zero on success or negative on error. + * Returns node ID of the next node on success or negative error code. */ static int __init split_nodes_size_interleave_uniform(struct numa_meminfo *ei, struct numa_meminfo *pi, @@ -398,7 +398,7 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt) */ if (strchr(emu_cmdline, 'U')) { unsigned long n; - int nid = 0; + int nid = 0, nr_created; n = simple_strtoul(emu_cmdline, &emu_cmdline, 0); ret = -1; @@ -416,9 +416,18 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt) n, &pi.blk[0], nid); if (ret < 0) break; - if (ret < n) { + + /* + * If no memory was found for this physical node, + * skip the under-allocation check. + */ + if (ret == nid) + continue; + + nr_created = ret - nid; + if (nr_created < n) { pr_info("%s: phys: %d only got %d of %ld nodes, failing\n", - __func__, i, ret, n); + __func__, i, nr_created, n); ret = -1; break; }