* Re: [RFC v2 PATCH] reserve_mem: add support for static memory
[not found] ` <ajyC2eX9MKSU84Z8@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
@ 2026-06-25 8:37 ` Mike Rapoport
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From: Mike Rapoport @ 2026-06-25 8:37 UTC (permalink / raw)
To: Shyam Saini
Cc: linux-mm, linux-doc, linux-kernel, akpm, tgopinath, bboscaccy,
kees, tony.luck, gpiccoli, bp, rdunlap, peterz, feng.tang,
dapeng1.mi, elver, enelsonmoore, kuba, lirongqing, ebiggers,
Catalin Marinas, Will Deacon, Ard Biesheuvel, David Hildenbrand,
linux-arm-kernel
Hi Shyam,
On Wed, Jun 24, 2026 at 06:22:33PM -0700, Shyam Saini wrote:
> On 21 Jun 2026 13:36, Mike Rapoport wrote:
> > On Thu, Jun 18, 2026 at 11:23:31PM -0700, Shyam Saini wrote:
> > > reserve_mem relies on dynamic memory allocation, this limits the
> > > usecase where memory is required to be preserved across the boots.
> > > Eg: ramoops memory reservation on ACPI platforms
> > >
> > > So add support to pass a pre-determined static address and reserve
> > > memory at a specified location. This enables use case like ramoops
> > > on ACPI platforms to reliably access ramoops region with previous
> > > boot logs.
> > >
> > > Also skip the parsing of <align> when static address is passed.
> > >
> > > Example syntax for static address
> > > reserve_mem=4M@0x1E0000000:oops
> >
> > reserve_mem is best effort by design because such hacks as well as memmap=
> > cannot guarantee this memory is actually free.
> >
> > If you want to preserve ramoops reliably, use KHO with reserve_mem.
> > The first kernel will allocate memory, this memory will be preserved by KHO
> > and could be picked up by the second kernel.
>
> ok, On ARM64 DTS systems, we can reserve ramoops memory in the device tree during
> the warm reboot.
The cc list actually implied x86 ;-)
Added arm64 folks now.
> For an equivalent ARM64 ACPI platform, what is the recommended way to reserve
> and preserve that memory across the boots?
I don't think it exists, but a command line option (be it memmap= or
reserve_mem=) does not seem the right way to me.
Most of the arguments that were made against adding memmap= to arm64 [1]
apply here.
If kexec is an option, KHO provides a reliable way to preserve memory
across boots.
If kexec is not an option, we should look for a generic way to specify
something like DT's reserved_mem for ACPI/EFI systems.
[1] https://lkml.kernel.org/lkml/20201118063314.22940-1-song.bao.hua@hisilicon.com/T/
> Thanks,
> Shyam
--
Sincerely yours,
Mike.
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