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

[Youling Tang]

On 4/15/26 19:29, Baoquan He wrote:

> On 04/09/26 at 09:55am, Youling Tang wrote:
> > Hi, Baoquan
> >
> > On 4/8/26 21:32, Baoquan He wrote:
> > > 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@xxxxxxxxxx>
> > > > >
> > > > > 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?
> > Yes, regular users generally don't know about high memory and low memory,
> > and probably don't know how much crashkernel memory should be reserved
> > either. They mostly just use the default crashkernel parameters configured
> > by the distribution.
> >
> > For advanced users, the current grammar is sufficient, because
> > 'crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset],>boundary'
> > can definitely be replaced with 'crashkernel=size,high'.
> >
> > The main purpose of this patch is to provide distributions with a more
> > reasonable default parameter configuration (satisfying most requirements),
> > without having to set different distribution default parameters for
> > different
> > scenarios (physical machines, virtual machines) and different machine
> > models.
> OK, do you have a concrete case? e.g in your distros, what will you set
> with this patchset applied? Let's see if it can cover all cases with one
> simple and satisfying parameter.

For our production deployment across various hardware configurations
(physical servers, VMs with different memory sizes), I'm planning to
use the following crashkernel configuration:
crashkernel=1G-4G:256M,4G-12G:384M,12G-48G:512M,48G-128G:768M,128G-:1024M,>384M

Thanks,
Youling.