[PATCH v2 0/5] kdump: crashkernel reservation from CMA

[David Hildenbrand]

On 30.05.25 11:26, Michal Hocko wrote:
> On Fri 30-05-25 11:11:40, David Hildenbrand wrote:
>> On 30.05.25 11:07, Michal Hocko wrote:
>>> On Fri 30-05-25 10:39:39, David Hildenbrand wrote:
>>>> On 30.05.25 10:28, Michal Hocko wrote:
>>> [...]
>>>>> All that being said I would go with an additional parameter to the
>>>>> kdump cma setup - e.g. cma_sane_dma that would skip waiting and use 10s
>>>>> otherwise. That would make the optimized behavior opt in, we do not need
>>>>> to support all sorts of timeouts and also learn if this is not
>>>>> sufficient.
>>>>>
>>>>> Makes sense?
>>>>
>>>> Just so I understand correctly, you mean extending the "crashkernel=" option
>>>> with a boolean parameter? If set, e.g., wait 1s, otherwise magic number 10?
>>>
>>> crashkernel=1G,cma,cma_sane_dma # no wait on transition
>>
>> But is no wait ok? I mean, any O_DIRECT with any device would at least take
>> a bit, no?
>>
>> Of course, there is a short time between the crash and actually triggerying
>> kdump.
> 
> This is something we can test for and if we need a short timeout in this
> case as well then it is just trivial to add it. I am much more
> concerned about those potentially unpredictable DMA transfers that could
> take too long and it is impossible to test for those and therefore we
> need to overshoot.

Agreed.

-- 
Cheers,

David / dhildenb