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SubjectRe: [tip: sched/core] sched/numa: Avoid migrating task to CPU-less node
Date
Hi, Qian,

"Huang, Ying" <ying.huang@intel.com> writes:

> Qian Cai <quic_qiancai@quicinc.com> writes:
>
>> On Thu, Feb 17, 2022 at 06:56:52PM -0000, tip-bot2 for Huang Ying wrote:
>>> The following commit has been merged into the sched/core branch of tip:
>>>
>>> Commit-ID: 5c7b1aaf139dab5072311853bacc40fc3457d1f9
>>> Gitweb: https://git.kernel.org/tip/5c7b1aaf139dab5072311853bacc40fc3457d1f9
>>> Author: Huang Ying <ying.huang@intel.com>
>>> AuthorDate: Mon, 14 Feb 2022 20:15:53 +08:00
>>> Committer: Peter Zijlstra <peterz@infradead.org>
>>> CommitterDate: Wed, 16 Feb 2022 15:57:53 +01:00
>>>
>>> sched/numa: Avoid migrating task to CPU-less node
>>>
>>> In a typical memory tiering system, there's no CPU in slow (PMEM) NUMA
>>> nodes. But if the number of the hint page faults on a PMEM node is
>>> the max for a task, The current NUMA balancing policy may try to place
>>> the task on the PMEM node instead of DRAM node. This is unreasonable,
>>> because there's no CPU in PMEM NUMA nodes. To fix this, CPU-less
>>> nodes are ignored when searching the migration target node for a task
>>> in this patch.
>>>
>>> To test the patch, we run a workload that accesses more memory in PMEM
>>> node than memory in DRAM node. Without the patch, the PMEM node will
>>> be chosen as preferred node in task_numa_placement(). While the DRAM
>>> node will be chosen instead with the patch.
>>>
>>> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>>> Link: https://lkml.kernel.org/r/20220214121553.582248-2-ying.huang@intel.com
>>
>> Reverting this commit on the top of today's linux-next fixed a boot crash
>> on arm64 NUMA systems.
>>
>> Unable to handle kernel paging request at virtual address ffff7a6601694aec
>> KASAN: maybe wild-memory-access in range [0xffffd3300b4a5760-0xffffd3300b4a5767]
>> Mem abort info:
>> ESR = 0x96000005
>> EC = 0x25: DABT (current EL), IL = 32 bits
>> mlx5_core 0007:02:00.0: enabling device (0100 -> 0102)
>> SET = 0, FnV = 0
>> EA = 0, S1PTW = 0
>> FSC = 0x05: level 1 translation fault
>> Data abort info:
>> ISV = 0, ISS = 0x00000005
>> CM = 0, WnR = 0
>> swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000400b3d6c6000
>> [ffff7a6601694aec] pgd=0000403fc007f003, p4d=0000403fc007f003, pud=0000000000000000
>> Internal error: Oops: 96000005 [#1] PREEMPT SMP
>> Modules linked in: nouveau(+) drm_ttm_helper ttm nvme(+) drm_dp_helper drm_kms_helper mlx5_core(+) mpt3sas(+) xhci_pci(+) nvme_core raid_class xhci_pci_renesas drm
>> CPU: 85 PID: 1308 Comm: udevadm Not tainted 5.17.0-rc6-next-20220301 #1
>> pstate: 40400009 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>> pc : task_numa_placement
>> lr : task_numa_placement
>> sp : ffff800031047760
>> x29: ffff800031047760 x28: ffff3fffab916c00 x27: 0000000000000020
>> x26: 0000000000000001 x25: 0000000000000000 x24: 0000000000000000
>>
>> x23: ffff07ffe5289a80 x22: ffffd3300b4a5760 x21: 000000000000003f
>> x20: ffffd32feb4a5768 x19: 0000000000000000 x18: ffff07ffe528ad88
>> x17: ffffd32fe5693a1c x16: 0000000000000000 x15: ffff8000310478e0
>>
>> x14: ffff07ffe528ad90 x13: 0000000000000002 x12: dfff80000000000d
>> x11: 0000000000000001 x10: 000000000000b6be x9 : 0000000000000000
>> x8 : 00000000ffffffff x7 : ffffd32feb4a5780 x6 : 0000000000000000
>> x5 : 0000000000000000 x4 : 0000000000000000 x3 : 1ffffa6601694aec
>> x2 : 0000000000000000 x1 : dfff800000000000 x0 : 000000001ffffff8
>> Call trace:
>> task_numa_placement
>> arch_test_bit at include/asm-generic/bitops/non-atomic.h:118
>> (inlined by) node_state at include/linux/nodemask.h:416
>> (inlined by) task_numa_placement at kernel/sched/fair.c:2439
>> task_numa_fault
>> do_numa_page
>> handle_pte_fault
>> __handle_mm_fault
>> handle_mm_fault
>> do_page_fault
>> do_translation_fault
>> do_mem_abort
>> el0_da
>> el0t_64_sync_handler
>> el0t_64_sync
>> Code: 8b000296 d2d00001 f2fbffe1 d343fec3 (38e16861)
>> ---[ end trace 0000000000000000 ]---
>> Kernel panic - not syncing: Oops: Fatal exception
>> SMP: stopping secondary CPUs
>> Kernel Offset: 0x532fdcf70000 from 0xffff800008000000
>> PHYS_OFFSET: 0x80000000
>> CPU features: 0x00,00042c0c,19801c82
>> Memory Limit: none
>> ---[ end Kernel panic - not syncing: Oops: Fatal exception ]---
>
> Thanks for reporting! Can you try whether the following debug patch can fix the issue?
>
> Best Regards,
> Huang, Ying
>
> ----------------------------8<-------------------------------------------
> From 176d185426730111e763eb386d0210561f021dbc Mon Sep 17 00:00:00 2001
> From: Huang Ying <ying.huang@intel.com>
> Date: Wed, 2 Mar 2022 08:54:01 +0800
> Subject: [PATCH] dbg KASAN error
>
> ---
> kernel/sched/fair.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a3f0ea216ccb..1fe7a4510cca 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2405,7 +2405,7 @@ static void task_numa_placement(struct task_struct *p)
> }
>
> /* Cannot migrate task to CPU-less node */
> - if (!node_state(max_nid, N_CPU)) {
> + if (max_nid != NUMA_NO_NODE && !node_state(max_nid, N_CPU)) {
> int near_nid = max_nid;
> int distance, near_distance = INT_MAX;

Do you have time to give this patch a try?

Best Regards,
Huang, Ying

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