Re: Frequent oom introduced in mainline when migrate_highatomic replace migrate_reserve

[zhong jiang <zhongjiang@huawei.com>]

On 2019/6/25 1:54, Michal Hocko wrote:
> On Tue 25-06-19 00:47:11, zhong jiang wrote:
>> On 2019/6/24 22:01, Michal Hocko wrote:
>>> On Mon 24-06-19 21:11:55, zhong jiang wrote:
>>>> [  652.272622] sh invoked oom-killer: gfp_mask=0x26080c0, order=3, oom_score_adj=0
>>>> [  652.272683] CPU: 0 PID: 1748 Comm: sh Tainted: P           O    4.4.171 #8
>>>> [  653.452827] Mem-Info:
>>>> [  653.466390] active_anon:20377 inactive_anon:187 isolated_anon:0
>>>> [  653.466390]  active_file:5087 inactive_file:4825 isolated_file:0
>>>> [  653.466390]  unevictable:12 dirty:0 writeback:32 unstable:0
>>>> [  653.466390]  slab_reclaimable:636 slab_unreclaimable:1754
>>>> [  653.466390]  mapped:5338 shmem:194 pagetables:231 bounce:0
>>>> [  653.466390]  free:1086 free_pcp:85 free_cma:0
>>>> [  653.625286] Normal free:4248kB min:1696kB low:2120kB high:2544kB active_anon:81508kB inactive_anon:748kB active_file:20348kB inactive_file:19300kB unevictable:48kB isolated(anon):0kB isolated(file):0kB present:252928kB managed:180496kB mlocked:0kB dirty:0kB writeback:128kB mapped:21352kB shmem:776kB slab_reclaimable:2544kB slab_unreclaimable:7016kB kernel_stack:9856kB pagetables:924kB unstable:0kB bounce:0kB free_pcp:392kB local_pcp:392kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
>>>> [  654.177121] lowmem_reserve[]: 0 0 0
>>>> [  654.462015] Normal: 752*4kB (UME) 128*8kB (UM) 21*16kB (M) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 4368kB
>>>> [  654.601093] 10132 total pagecache pages
>>>> [  654.606655] 63232 pages RAM
>>> [...]
>>>>>> As the process is created,  kernel stack will use the higher order to allocate continuous memory.
>>>>>> Due to the fragmentabtion,  we fails to allocate the memory.   And the low memory will result
>>>>>> in hardly memory compction.  hence,  it will easily to reproduce the oom.
>>>>> How get your get such a large fragmentation that you cannot allocate
>>>>> order-1 pages and compaction is not making any progress?
>>>> >From the above oom report,  we can see that  there is not order-2 pages.  It wil hardly to allocate kernel stack when
>>>> creating the process.  And we can easily to reproduce the situation when runing some userspace program.
>>>>
>>>> But it rarely trigger the oom when It do not introducing the highatomic.  we test that in the kernel 3.10.
>>> I do not really see how highatomic reserves could make any difference.
>>> We do drain them before OOM killer is invoked. The above oom report
>>> confirms that there is indeed no order-3+ free page to be used.
>> I mean that all order with migrate_highatomic is alway zero,  it can be  true that
> Yes, highatomic is meant to be used for higher order allocations which
> already do have access to memory reserves. E.g. via __GFP_ATOMIC.
If current kernel have not use __GFP_ATOMIC to allocate memory,  highatomic will have not available higher order.
And we have order-3 kernel stack allocation requirement in the system.  

There is not  memory reserve to use for us in the emergency situation,  which is different from migrate_reserve.
Maybe I  think that we can change the reserve memory behaviour,  Not only reserve higher order in GFP_ATOMIC.

Thanks,
zhong jiang