From: Mike Rapoport <rppt@kernel.org>
To: Shyam Saini <shyamsaini@linux.microsoft.com>
Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
tgopinath@linux.microsoft.com, bboscaccy@linux.microsoft.com,
kees@kernel.org, tony.luck@intel.com, gpiccoli@igalia.com,
bp@alien8.de, rdunlap@infradead.org, peterz@infradead.org,
feng.tang@linux.alibaba.com, dapeng1.mi@linux.intel.com,
elver@google.com, enelsonmoore@gmail.com, kuba@kernel.org,
lirongqing@baidu.com, ebiggers@kernel.org,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
David Hildenbrand <david@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC v2 PATCH] reserve_mem: add support for static memory
Date: Thu, 25 Jun 2026 11:37:18 +0300 [thread overview]
Message-ID: <ajzovhWHcFQZ9d3l@kernel.org> (raw)
In-Reply-To: <ajyC2eX9MKSU84Z8@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
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.
prev parent reply other threads:[~2026-06-25 8:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-19 6:23 [RFC v2 PATCH] reserve_mem: add support for static memory Shyam Saini
2026-06-19 18:35 ` Randy Dunlap
2026-06-25 1:09 ` Shyam Saini
2026-06-21 10:36 ` Mike Rapoport
2026-06-25 1:22 ` Shyam Saini
2026-06-25 8:37 ` Mike Rapoport [this message]
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