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Peter Anvin" , Ingo Molnar , Michal Hocko , Mike Rapoport , Peter Zijlstra , Qi Zheng , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] x86/mm: drop 4MB restriction on minimal NUMA node size Date: Tue, 17 Oct 2023 09:22:15 +0300 Message-Id: <20231017062215.171670-1-rppt@kernel.org> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: "Mike Rapoport (IBM)" Qi Zheng reports crashes in a production environment and provides a simplified example as a reproducer: For example, if we use qemu to start a two NUMA node kernel, one of the nodes has 2M memory (less than NODE_MIN_SIZE), and the other node has 2G, then we will encounter the following panic: [ 0.149844] BUG: kernel NULL pointer dereference, address: 00000000000= 00000 [ 0.150783] #PF: supervisor write access in kernel mode [ 0.151488] #PF: error_code(0x0002) - not-present page <...> [ 0.156056] RIP: 0010:_raw_spin_lock_irqsave+0x22/0x40 <...> [ 0.169781] Call Trace: [ 0.170159] [ 0.170448] deactivate_slab+0x187/0x3c0 [ 0.171031] ? bootstrap+0x1b/0x10e [ 0.171559] ? preempt_count_sub+0x9/0xa0 [ 0.172145] ? kmem_cache_alloc+0x12c/0x440 [ 0.172735] ? bootstrap+0x1b/0x10e [ 0.173236] bootstrap+0x6b/0x10e [ 0.173720] kmem_cache_init+0x10a/0x188 [ 0.174240] start_kernel+0x415/0x6ac [ 0.174738] secondary_startup_64_no_verify+0xe0/0xeb [ 0.175417] [ 0.175713] Modules linked in: [ 0.176117] CR2: 0000000000000000 The crashes happen because of inconsistency between nodemask that has nodes with less than 4MB as memoryless and the actual memory fed into core mm. The commit 9391a3f9c7f1 ("[PATCH] x86_64: Clear more state when ignoring empty node in SRAT parsing") that introduced minimal size of a NUMA node does not explain why a node size cannot be less than 4MB and what boot failures this restriction might fix. Since then a lot has changed and core mm won't confuse badly about small node sizes. Drop the limitation for the minimal node size. Reported-by: Qi Zheng Signed-off-by: Mike Rapoport (IBM) Acked-by: David Hildenbrand Acked-by: Michal Hocko Link: https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@byted= ance.com/ Tested-by: Mario Casquero --- arch/x86/include/asm/numa.h | 7 ------- arch/x86/mm/numa.c | 7 ------- 2 files changed, 14 deletions(-) diff --git a/arch/x86/include/asm/numa.h b/arch/x86/include/asm/numa.h index e3bae2b60a0d..ef2844d69173 100644 --- a/arch/x86/include/asm/numa.h +++ b/arch/x86/include/asm/numa.h @@ -12,13 +12,6 @@ =20 #define NR_NODE_MEMBLKS (MAX_NUMNODES*2) =20 -/* - * Too small node sizes may confuse the VM badly. Usually they - * result from BIOS bugs. So dont recognize nodes as standalone - * NUMA entities that have less than this amount of RAM listed: - */ -#define NODE_MIN_SIZE (4*1024*1024) - extern int numa_off; =20 /* diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c index 2aadb2019b4f..55e3d895f15c 100644 --- a/arch/x86/mm/numa.c +++ b/arch/x86/mm/numa.c @@ -601,13 +601,6 @@ static int __init numa_register_memblks(struct numa_me= minfo *mi) if (start >=3D end) continue; =20 - /* - * Don't confuse VM with a node that doesn't have the - * minimum amount of memory: - */ - if (end && (end - start) < NODE_MIN_SIZE) - continue; - alloc_node_data(nid); } =20 base-commit: 94f6f0550c625fab1f373bb86a6669b45e9748b3 --=20 2.39.2