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Thu, 22 Oct 2026 00:04:17 -0700 (PDT) Received: from [10.125.112.22] ([122.11.210.25]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ea3b43478csm19901295ad.28.2026.10.22.00.04.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 Oct 2026 00:04:16 -0700 (PDT) Message-ID: <95f18ef2-8fda-447e-bc64-1732febea363@gmail.com> Date: Thu, 22 Oct 2026 15:04:02 +0800 X-Mailing-List: iommu@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 0/8] kdump: reduce vmcore size and capture time To: Rob Herring , "rppt@kernel.org" Cc: baoquan.he@linux.dev, m.szyprowski@samsung.com, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, chenhuacai@kernel.org, kernel@xen0n.name, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, saravanak@kernel.org, akpm@linux-foundation.org, pasha.tatashin@soleen.com, pratyush@kernel.org, ruirui.yang@linux.dev, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org, iommu@lists.linux.dev References: <20261021083011.2170525-1-chenwandun1@gmail.com> <20261021132308.GB3667411-robh@kernel.org> Content-Language: en-US From: Wandun In-Reply-To: <20261021132308.GB3667411-robh@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/21/26 21:23, Rob Herring wrote: > On Wed, Oct 21, 2026 at 04:30:03PM +0800, Wandun Chen wrote: >> From: Wandun Chen >> >> On SoCs that carve out large firmware-owned reserved memory (GPU, >> camera ISP, ...), kdump currently dumps those carveouts as part of >> system RAM even though their contents are firmware state that is not >> useful for kernel crash analysis. >> >> ACPI systems already filter reserved memory out of the vmcore through >> their existing path: firmware reports those carveouts as unusable in >> the EFI memory map, they get MEMBLOCK_NOMAP set in memblock.memory >> (is_usable_memory(), efi-init.c), and the ELF header builder has >> always skipped nomap regions; only DT-based systems currently fail >> to filter these regions, which is what this series addresses. >> >> This series introduces a MEMBLOCK_NODUMP flag (suggested by Rob) in >> memblock to filter reserved memory on DT-based architectures. A new >> flag is needed because MEMBLOCK_NOMAP can only express regions without >> a linear mapping, while MEMBLOCK_NODUMP can filter regions that are >> linearly mapped. Reserved regions are marked MEMBLOCK_NODUMP by default >> so kdump omits them; reusable CMA regions are different because their >> pages are handed back to the buddy allocator and may carry crash-relevant >> data. > > There is little point in continuing to send new versions until Mike > agrees with MEMBLOCK_NODUMP being added. You didn't answer him on v7. Hi Rob, Thanks for the reminder. On v7 your reply to Mike stated exactly what I wanted to say, after a week without further objections, so I assumed the question was settled and went ahead with next version. That was a mistake on my part: I should have gotten Mike's agreement on the flag before sending a new version. I'll hold off further versions until then. Hi Mike, Sorry for not following up on your v7 question. The reason a new flag is needed is described in the v9 cover letter: A new flag is needed because MEMBLOCK_NOMAP can only express regions without a linear mapping, while MEMBLOCK_NODUMP can filter regions that are linearly mapped. Put differently: today, whether a region ends up in the vmcore is a side effect of how it is mapped, mapped regions are always dumped, nomap regions never are. Nothing can express "mapped, but not useful in a crash dump". MEMBLOCK_NODUMP decouples the two, and DT is simply the first user. > > Also, I intend to apply this[1] before any further reserved memory > changes which will greatly simplify the code. Understood, and it makes sense. It removes the two-pass reserved_mem initialization and indeed simplify the code, I'll rebase on top of it once it lands; Best regards, Wandun > > Rob > > [1] https://lore.kernel.org/all/20261015082315.56876-1-m.szyprowski@samsung.com/