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([2a02:6b6f:e750:1800:450:cba3:aec3:a1fd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4790adc6f7bsm122263015e9.2.2025.11.27.13.04.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 27 Nov 2025 13:04:59 -0800 (PST) Message-ID: <56673a9c-a4c9-4962-baec-2d4483af3cfa@gmail.com> Date: Thu, 27 Nov 2025 21:04:58 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] mm/memblock: only mark/clear KHO scratch memory when needed Content-Language: en-GB To: Andrew Morton Cc: rppt@kernel.org, kas@kernel.org, changyuanl@google.com, graf@amazon.com, leitao@debian.org, thevlad@meta.com, pratyush@kernel.org, dave.hansen@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20251127203724.3177621-1-usamaarif642@gmail.com> <20251127203724.3177621-3-usamaarif642@gmail.com> <20251127125539.98b2f148c6225f1cb7c9d045@linux-foundation.org> From: Usama Arif In-Reply-To: <20251127125539.98b2f148c6225f1cb7c9d045@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: nas4yitgethr9kxto5nezhk96wpq8n1f X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D8162A0018 X-HE-Tag: 1764277501-949897 X-HE-Meta: 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 sfrVgwWL 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27/11/2025 20:55, Andrew Morton wrote: > On Thu, 27 Nov 2025 20:33:20 +0000 Usama Arif wrote: > >> The scratch memory for kexec handover is used to bootstrap the >> kexec'ed kernel. It is only needed when CONFIG_KEXEC_HANDOVER >> is enabled and only if it is a KHO boot. Add checks to prevent >> marking a KHO scratch region unless needed. > > What effect does this change have? Lessened memory consumption, > presumably. Of what magnitude and for what time period? For some context, this came out of https://lore.kernel.org/all/ba690e06-c2a1-4d2e-9428-9ca2ea9f2b86@gmail.com/ (I should have probably added that in the commit message..) We are experiencing several warnings a day in meta fleet due to a warning introduced in that patch. We dont have CONFIG_KEXEC_HANDOVER enabled in the fleet. The IMA memory seems to conincide with the 1st MB, but as Mike pointed out they are different arrays so this scratch memory is likely not a cause of the warnings. But it is not useful (and was a bit confusing) seeing KHO scratch memory being marked even when KHO is disabled. The imapct is as you said, but its only marked for a very short period of time. I think a better reason for this patch is just to not mark the memory at all when KHO is disabled (or not in use) for clarity.