Re: [PATCH] crash: Support high memory reservation for range syntax

Baoquan He
2026-04-08T13:33:09Z

On 04/08/26 at 10:01am, Sourabh Jain wrote:
> Hello Youling,
>
> On 04/04/26 13:11, Youling Tang wrote:
> > From: Youling Tang <tangyouling@kylinos.cn>
> >
> > The crashkernel range syntax (range1:size1[,range2:size2,...]) allows
> > automatic size selection based on system RAM, but it always reserves
> > from low memory. When a large crashkernel is selected, this can
> > consume most of the low memory, causing subsequent hardware
> > hotplug or drivers requiring low memory to fail due to allocation
> > failures.
>
>
> Support for high crashkernel reservation has been added to
> address the above problem.
>
> However, high crashkernel reservation is not supported with
> range-based crashkernel kernel command-line arguments.
> For example: crashkernel=0M-1G:100M,1G-4G:160M,4G-8G:192M
>
> Many users, including some distributions, use range-based
> crashkernel configuration. So, adding support for high crashkernel
> reservation with range-based configuration would be useful.

Sorry for late response. And I have to say sorry because I have some
negative tendency on this change.

We use crashkernel=xM|G and crashkernel=range1:size1[,range2:size2,...]
as default setting, so that people only need to set suggested amount
of memory. While crashkernel=,high|low is for advanced user to customize
their crashkernel value. In that case, user knows what's high memory and
low memory, and how much is needed separately to achieve their goal, e.g
saving low memory, taking away more high memory.

To be honest, above grammers sounds simple, right? I believe both of you
know very well how complicated the current crashkernel code is. I would
suggest not letting them becomre more and more complicated by extending
the grammer further and further. Unless you meet unavoidable issue with
the existing grammer.

Here comes my question, do you meet unavoidable issue with the existing
grammer when you use crashkernel=range1:size1[,range2:size2,...] and
think it's not satisfactory, and at the same time crashkernel=,high|low
can't meet your demand either?

Thanks
Baoquan