Re: [PATCH 1/1] mm/page_alloc: add scheduling point to free_unref_page_list

[wangjianxing <wangjianxing@loongson.cn>]

On 03/03/2022 07:34 AM, Andrew Morton wrote:
> On Tue,  1 Mar 2022 20:38:25 -0500 wangjianxing <wangjianxing@loongson.cn> wrote:
>
>> free a large list of pages maybe cause rcu_sched starved on
>> non-preemptible kernels
>>
>> rcu: rcu_sched kthread starved for 5359 jiffies! g454793 f0x0
>> RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=19
>> [...]
>> Call Trace:
>>    free_unref_page_list+0x19c/0x270
>>    release_pages+0x3cc/0x498
>>    tlb_flush_mmu_free+0x44/0x70
>>    zap_pte_range+0x450/0x738
>>    unmap_page_range+0x108/0x240
>>    unmap_vmas+0x74/0xf0
>>    unmap_region+0xb0/0x120
>>    do_munmap+0x264/0x438
>>    vm_munmap+0x58/0xa0
>>    sys_munmap+0x10/0x20
>>    syscall_common+0x24/0x38
> Thanks.
>
> How did this large list of pages come about?
>
> Will people be seeing this message in upstream kernels, or is it
> specific to some caller code which you have added?
>
> Please always include details such as this so that others can determine
> whether the fix should be backported into -stable kernels.
Thanks.

I try to increase the overcommit ratio of cpu to 1:2~1:3 in KVM 
hypervisor, per-vm has the same number of vcpu with host cpu, then setup 
2 or 3 vm.
Run ltpstress test in per vm, both host and guest is non-preemptiable 
kernel, vm dmesg will throw some rcu_sched warning.

ltp version is 20180926, but until now I didn't analysis ltpstress code 
deeply.