Re: Suspicious error for CMA stress test

Hanjun Guo
2016-03-03T07:58:47Z

On 2016/3/3 15:42, Joonsoo Kim wrote:
> 2016-03-03 10:25 GMT+09:00 Laura Abbott <labbott@redhat.com>:
>> (cc -mm and Joonsoo Kim)
>>
>>
>> On 03/02/2016 05:52 AM, Hanjun Guo wrote:
>>> Hi,
>>>
>>> I came across a suspicious error for CMA stress test:
>>>
>>> Before the test, I got:
>>> -bash-4.3# cat /proc/meminfo | grep Cma
>>> CmaTotal: 204800 kB
>>> CmaFree: 195044 kB
>>>
>>>
>>> After running the test:
>>> -bash-4.3# cat /proc/meminfo | grep Cma
>>> CmaTotal: 204800 kB
>>> CmaFree: 6602584 kB
>>>
>>> So the freed CMA memory is more than total..
>>>
>>> Also the the MemFree is more than mem total:
>>>
>>> -bash-4.3# cat /proc/meminfo
>>> MemTotal: 16342016 kB
>>> MemFree: 22367268 kB
>>> MemAvailable: 22370528 kB
>>>
>>> Here is the kernel module doing the stress test below (if the test case
>>> is wrong, correct me), any help would be great appreciated.
>>>
>>> The test is running on ARM64 platform (hisilicon D02) with 4.4 kernel, I
>>> think
>>> the 4.5-rc is the same as I didn't notice the updates for it.
>>>
>>> int malloc_dma(void *data)
>>> {
>>> void *vaddr;
>>> struct platform_device * pdev=(struct platform_device*)data;
>>> dma_addr_t dma_handle;
>>> int i;
>>>
>>> for(i=0; i<1000; i++) {
>>> vaddr=dma_alloc_coherent(&pdev->dev, malloc_size, &dma_handle,
>>> GFP_KERNEL);
>>> if (!vaddr)
>>> pr_err("alloc cma memory failed!\n");
>>>
>>> mdelay(1);
>>>
>>> if (vaddr)
>>> dma_free_coherent(&pdev->dev,malloc_size,vaddr,
>>> dma_handle);
>>> }
>>> pr_info("alloc free cma memory success return!\n");
>>> return 0;
>>> }
>>>
>>> static int dma_alloc_coherent_init(struct platform_device *pdev)
>>> {
>>> int i;
>>>
>>> for(i=0; i<100; i++) {
>>> task[i] = kthread_create(malloc_dma,pdev,"malloc_dma_%d",i);
>>> if(!task[i]) {
>>> printk("kthread_create faile %d\n",i);
>>> continue;
>>> }
>>> wake_up_process(task[i]);
>>> }
>>> return 0;
>>> }
>>>
>>> Thanks
>>> Hanjun
>>>
>>> The whole /proc/meminfo:
>>>
>>> -bash-4.3# cat /proc/meminfo
>>> MemTotal: 16342016 kB
>>> MemFree: 22367268 kB
>>> MemAvailable: 22370528 kB
>>> Buffers: 4292 kB
>>> Cached: 36444 kB
>>> SwapCached: 0 kB
>>> Active: 23564 kB
>>> Inactive: 25360 kB
>>> Active(anon): 8424 kB
>>> Inactive(anon): 64 kB
>>> Active(file): 15140 kB
>>> Inactive(file): 25296 kB
>>> Unevictable: 0 kB
>>> Mlocked: 0 kB
>>> SwapTotal: 0 kB
>>> SwapFree: 0 kB
>>> Dirty: 0 kB
>>> Writeback: 0 kB
>>> AnonPages: 8196 kB
>>> Mapped: 16448 kB
>>> Shmem: 296 kB
>>> Slab: 26832 kB
>>> SReclaimable: 6300 kB
>>> SUnreclaim: 20532 kB
>>> KernelStack: 3088 kB
>>> PageTables: 404 kB
>>> NFS_Unstable: 0 kB
>>> Bounce: 0 kB
>>> WritebackTmp: 0 kB
>>> CommitLimit: 8171008 kB
>>> Committed_AS: 34336 kB
>>> VmallocTotal: 258998208 kB
>>> VmallocUsed: 0 kB
>>> VmallocChunk: 0 kB
>>> AnonHugePages: 0 kB
>>> CmaTotal: 204800 kB
>>> CmaFree: 6602584 kB
>>> HugePages_Total: 0
>>> HugePages_Free: 0
>>> HugePages_Rsvd: 0
>>> HugePages_Surp: 0
>>> Hugepagesize: 2048 kB
>>>
>>
>> I played with this a bit and can see the same problem. The sanity
>> check of CmaFree < CmaTotal generally triggers in
>> __move_zone_freepage_state in unset_migratetype_isolate.
>> This also seems to be present as far back as v4.0 which was the
>> first version to have the updated accounting from Joonsoo.
>> Were there known limitations with the new freepage accounting,
>> Joonsoo?
> I don't know. I also played with this and looks like there is
> accounting problem, however, for my case, number of free page is slightly less
> than total. I will take a look.
>
> Hanjun, could you tell me your malloc_size? I tested with 1 and it doesn't
> look like your case.

The malloc_size is 1M, and with 200M total (passed via boot commandline cma=200M),
any more information is needed, please let me know.

Thanks for the help!
Hanjun