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

[Baoquan He]

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.