Re: Crash kernel with 256 MB reserved memory runs into OOM condition

[Paul Menzel]

Dear Dave,


Thank you for your replies.


On 2019-08-13 04:54, Dave Young wrote:
> On 08/13/19 at 10:46am, Dave Young wrote:

>> On 08/13/19 at 10:43am, Dave Young wrote:

>>> On 08/12/19 at 11:50am, Michal Hocko wrote:
>>>> On Mon 12-08-19 11:42:33, Paul Menzel wrote:

>>>>> On a Dell PowerEdge R7425 with two AMD EPYC 7601 (total 128 threads) and
>>>>> 1 TB RAM, the crash kernel with 256 MB of space reserved crashes.
>>>>>
>>>>> Please find the messages of the normal and the crash kernel attached.
>>>>
>>>> You will need more memory to reserve for the crash kernel because ...
>>>>
>>>>> [    4.548703] Node 0 DMA free:484kB min:4kB low:4kB high:4kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:568kB managed:484kB mlocked:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
>>>>> [    4.573612] lowmem_reserve[]: 0 125 125 125
>>>>> [    4.577799] Node 0 DMA32 free:1404kB min:1428kB low:1784kB high:2140kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:15720kB writepending:0kB present:261560kB managed:133752kB mlocked:0kB kernel_stack:2496kB pagetables:0kB bounce:0kB free_pcp:212kB local_pcp:212kB free_cma:0kB
>>>>
>>>> ... the memory is really depleted and nothing to be reclaimed (no anon.
>>>> file pages) Look how tht free memory is below min watermark (node zone DMA has
>>>> lowmem protection for GFP_KERNEL allocation).
>>>
>>> We found similar issue on our side while working on kdump on SME enabled
>>> systemd.  Kairui is working on some patches.
>>>
>>> Actually on those SME/SEV enabled machines, swiotlb is enabled
>>> automatically so at least we need extra 64M+ memory for kdump other
>>> than the normal expectation.
>>>
>>> Can you check if this is also your case?
>>
>> The question is to Paul,  also it would be always good to cc kexec mail
>> list for kexec and kdump issues.

As already replied <kexec@xxxxxxxxxxxxxxxxxxx> was CCed in my original
message, but the list put it under moderation.

> Looks like hardware iommu is used, maybe you do not enable SME?

Do you mean AMD Secure Memory Encryption? I do not think, we use that.

> Also replace maxcpus=1 with nr_cpus=1 can save some memory, can have a
> try.

Thank you for this suggestion. That fixed it indeed, and the reserved
memory can stay at 256 MB. (The parameter names are a little unintuitive â
I guess due to historical reasons.


Kind regards,

Paul


[1]: https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt

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