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SubjectRe: [RFC PATCH v2 0/3] pmem memmap dump support
Date
Dan,


On 29/04/2023 02:59, Dan Williams wrote:
> Li Zhijian wrote:
>> Hello folks,
>>
>> About 2 months ago, we posted our first RFC[3] and received your kindly feedback. Thank you :)
>> Now, I'm back with the code.
>>
>> Currently, this RFC has already implemented to supported case D*. And the case A&B is disabled
>> deliberately in makedumpfile. It includes changes in 3 source code as below:
>
> I think the reason this patchkit is difficult to follow is that it
> spends a lot of time describing a chosen solution, but not enough time
> describing the problem and the tradeoffs.
>
> For example why is updating /proc/vmcore with pmem metadata the chosen
> solution? Why not leave the kernel out of it and have makedumpfile
> tooling aware of how to parse persistent memory namespace info-blocks
> and retrieve that dump itself? This is what I proposed here:
>
> http://lore.kernel.org/r/641484f7ef780_a52e2940@dwillia2-mobl3.amr.corp.intel.com.notmuch

Sorry for the late reply. I'm just back from the vacation.
And sorry again for missing your previous *important* information in V1.

Your proposal also sounds to me with less kernel changes, but more ndctl coupling with makedumpfile tools.
In my current understanding, it will includes following source changes.

-----------+-------------------------------------------------------------------+
Source | changes |
-----------+-------------------------------------------------------------------+
I. | 1. enter force_raw in kdump kernel automatically(avoid metadata being updated again)|
kernel | |
| 2. mark the whole pmem's PT_LOAD for kexec_file_load(2) syscall |
-----------+-------------------------------------------------------------------+
II. kexec- | 1. mark the whole pmem's PT_LOAD for kexe_load(2) syscall |
tool | |
-----------+-------------------------------------------------------------------+
III. | 1. parse the infoblock and calculate the boundaries of userdata and metadata |
makedump- | 2. skip pmem userdata region |
file | 3. exclude pmem metadata region if needed |
-----------+-------------------------------------------------------------------+

I will try rewrite it with your proposal ASAP

Thanks again

Thanks
Zhijian

>
> ...but never got an answer, or I missed the answer.
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