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b=FGlFrAQy6E1uz0C3XgqICgDtpY4DNdRjgthseoT8MOaduXl+SL2fHnjmBcTYDYVoi aahon87kV8Efqxe2wgajqSOfG+M8UjxNNxFsy+F5zI+k++5To0Lok2H3O3Rv1rReCc 4GdaD1AQG03Ev/h+Ut1+huKOcnbWktK3QkMVU8PbwQ/NT4ysLrtbHE2zVbir4hs4P/ NrVHnpV8HVagJwIgz0sIcJXup1HvAIrniYojkT3EXswnjYmA8WlxJbIWl1GTzV1Wo9 uiKQORFPHRADJs5La5tVBgIZquUTMYRVkk8GBfS+6AZVOCWadOU7XYgpssTnjgx/Gv Xi0QONQ3Fwmug== Date: Thu, 25 Jun 2026 11:37:18 +0300 From: Mike Rapoport To: Shyam Saini 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 , Will Deacon , Ard Biesheuvel , David Hildenbrand , linux-arm-kernel@lists.infradead.org Subject: Re: [RFC v2 PATCH] reserve_mem: add support for static memory Message-ID: References: <20260619062331.348789-1-shyamsaini@linux.microsoft.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Stat-Signature: bid9hjp4o3bx8b8pqnykn7sz9x63qfb4 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 5805C8000A X-HE-Tag: 1782376650-253795 X-HE-Meta: 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 8TqbqM9Z S7h+N9dhHrYTSoLd+108HfjqbvqbTSL01aaOCuYQ2Vqp0KMf7kZRndeCpxYR/3sg3M2CRFLkPbJKjapPUdVNXyvlTsjwbRjJiy9KJsNKvct5JK9DZc9BgeYlB5EAEp7O7ASFGMlO6ghtLKK39hWk0Fd1f8s2dO/iCOs4iC28BYp1xARCJ3qwZ9oVEu+hqPlkMrbUEsN7UKDqT/ZRP1o0gbXoKe0Ijz5Zkw4QHRE8jUj+gq1jJvFeg3ClNo99/pdBNTdExBUga1X170p5e+u9DfspVFLt3Qk72VvUSFkxtzETUZTo4qteDkwlAeqs3oZrebNRmWCDoAJ+n5zqomm5en9nSLCuk6pI8qcEVNQXqLLL/rXTNP3V/ndjZfmsyBhoaVzdu Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 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.