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Wed, 04 Nov 2026 16:15:48 +0000 X-Mizu-Trace-ID: c6ae390f292ebaa1 X-Migadu-Flow: FLOW_OUT Message-ID: <81096741-0e14-4469-bdbb-497aba541fbb@linux.dev> Date: Wed, 4 Nov 2026 16:15:46 +0000 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/hugetlb: allow crashkernel to reuse hugetlb CMA memory To: Kiryl Shutsemau Cc: Andrew Morton , baoquan.he@linux.dev, rppt@kernel.org, pasha.tatashin@soleen.com, pratyush@kernel.org, ruirui.yang@linux.dev, corbet@lwn.net, skhan@linuxfoundation.org, rdunlap@infradead.org, muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, jbohac@suse.cz, sourabhjain@linux.ibm.com, ruanjinjie@huawei.com, leitao@debian.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, kernel-team@meta.com References: <20261104142727.2894800-1-usama.arif@linux.dev> Content-Language: en-US From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 27AAAC0014 X-Stat-Signature: docrbca74txdfzqwsogr51be4zrh4x45 X-Rspam-User: X-HE-Tag: 1793808951-488518 X-HE-Meta: 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 qtTXXQ4L wsgcKoXqkBoqcTsPl4Rtr2mxW5UnAIHfJJB28dHaqTZapmKARmgT3ecAiRmRL9o7nqdalqgoLLelLm51Sx1A3BkqTQI2ANd1cj/QV0TZNFTPGVMqpKmRKnvIb7+dHvrTzQeBQpqheKFqlOfnsApoUYpM/Uwr2NCw08gjXQ12t51TkOmv5IJZFEfg7/ehqkCS6En/duX+iuIuppQk7j42hR1rAMQIWp5zDj0gcIRCXT/P1m5sGozLDror28VWI5+qSRDsl0lWpZzADw1mG8/DGP5nmCg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 04/11/2026 15:20, Kiryl Shutsemau wrote: > On Wed, Nov 04, 2026 at 06:27:27AM -0800, Usama Arif wrote: >> Use a separate suffix to make the exclusion of existing HugeTLB >> allocations from the vmcore an explicit choice. > > The crashkernel=size,cma documentation already says that pages allocated > from the range are not in the vmcore and that it should not be used if > dumping of userspace memory is intended. HugeTLB pages are userspace > memory. I don't see what a new suffix makes explicit that ",cma" does > not already. > > Why not let crashkernel=size,cma take hugetlb CMA first and reserve a > dedicated area only for what hugetlb CMA does not cover? With > hugetlb_cma=6G crashkernel=2G,cma there would be no extra CMA at all. > With hugetlb_cma=2G crashkernel=4G,cma the crash kernel would reuse the > 2G and a dedicated 2G area would be reserved for the rest. Either way, > nobody has to learn a new option. > > The catch is ordering. reserve_crashkernel_cma() runs from setup_arch(), > but hugetlb_cma_reserve() runs later, from mm_core_init_early(). The arch > code could record the size and leave the reservation to generic code > right after hugetlb_cma_reserve(). That is still memblock time, so the > remainder can be declared there. An early_initcall is too late for that. > Makes sense to me, I will rewrite it in the above way and send v2. Thanks for the review! Usama