Re: [PATCH] mm/hugetlb: allow crashkernel to reuse hugetlb CMA memory

[Usama Arif <usama.arif@linux.dev>]

On 04/11/2026 15:20, Kiryl Shutsemau wrote:
> On Wed, Nov 04, 2026 at 06:27:27AM -0800, Usama Arif wrote:
>> Use a separate suffix to make the exclusion of existing HugeTLB
>> allocations from the vmcore an explicit choice.
> 
> The crashkernel=size,cma documentation already says that pages allocated
> from the range are not in the vmcore and that it should not be used if
> dumping of userspace memory is intended. HugeTLB pages are userspace
> memory. I don't see what a new suffix makes explicit that ",cma" does
> not already.
> 
> Why not let crashkernel=size,cma take hugetlb CMA first and reserve a
> dedicated area only for what hugetlb CMA does not cover? With
> hugetlb_cma=6G crashkernel=2G,cma there would be no extra CMA at all.
> With hugetlb_cma=2G crashkernel=4G,cma the crash kernel would reuse the
> 2G and a dedicated 2G area would be reserved for the rest. Either way,
> nobody has to learn a new option.
> 
> The catch is ordering. reserve_crashkernel_cma() runs from setup_arch(),
> but hugetlb_cma_reserve() runs later, from mm_core_init_early(). The arch
> code could record the size and leave the reservation to generic code
> right after hugetlb_cma_reserve(). That is still memblock time, so the
> remainder can be declared there. An early_initcall is too late for that.
> 

Makes sense to me, I will rewrite it in the above way and send v2.

Thanks for the review!
Usama