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[109.81.80.251]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-432449ae0ffsm4488541f8f.39.2025.12.18.04.17.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Dec 2025 04:17:26 -0800 (PST) Date: Thu, 18 Dec 2025 13:17:25 +0100 From: Michal Hocko To: Ryan Roberts Cc: Yeoreum Yun , akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org, catalin.marinas@arm.com, will@kernel.org, kevin.brodsky@arm.com, dev.jain@arm.com, yang@os.amperecomputing.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-rt-devel@lists.linux.dev, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 2/2] arm64: mmu: use pagetable_alloc_nolock() while stop_machine() Message-ID: References: <20251212161832.2067134-1-yeoreum.yun@arm.com> <20251212161832.2067134-3-yeoreum.yun@arm.com> <0d08b4bf-35c5-4c63-964b-ef886b8262d9@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0d08b4bf-35c5-4c63-964b-ef886b8262d9@arm.com> X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: DE614180017 X-Stat-Signature: qityqutfsqsxcryae3zcadj73gzyichf X-HE-Tag: 1766060247-320525 X-HE-Meta: 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 bh9aYjer wqmDfQQ+9XL9BiuiuO001RnYAxc2ypBBWYcYktsOllnywXGGyafetpAHLxAYtWEYhf1OfQ7Pq4ZYn54M7gcS4nCL38DSjzMTxEoZpzBxJrjy85VxoyrdD1LMiVWyuyE9oqe7exHWS1Eig9eHsMfjAWWP9G1afcNpIZrjfbKh4k7qOPyfBtxGa0lZlJp6/jVRFnB1glNgYHxu8GbSqh7M8YUD5W65RAYuYzPINfhM89CHzE3NLM0hDOicBpZz7iCHC0gpDtsIBNGUGnzypnem8AtkopKrFrZ0WYC6u7MAp6uXBAelr1brgrvnkDmWNJ+5dzjsHs4gVE06/cKP/Kd7XR2Ny2cRl9CCAxBFZHiHOeEVVmqqTgGQ09R9p5exEvFoASEO8ASjREg25pZPsno8o/btifPQ1kqH1uxZmIu/sa8RuumqCc4a6Hl2uaCsJ+VfByx5zVQwy++37G+wJIGU+6VFZNsT3OsyhH2dA 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 Thu 18-12-25 12:02:14, Ryan Roberts wrote: > On 18/12/2025 09:36, Yeoreum Yun wrote: > > Hi, > >> On Fri 12-12-25 16:18:32, Yeoreum Yun wrote: > >>> linear_map_split_to_ptes() and __kpti_install_ng_mappings() > >>> are called as callback of stop_machine(). > >>> That means these functions context are preemption disabled. > >>> > >>> Unfortunately, under PREEMPT_RT, the pagetable_alloc() or > >>> __get_free_pages() couldn't be called in this context > >>> since spin lock that becomes sleepable on RT, > >>> potentially causing a sleep during page allocation. > >>> > >>> To address this, pagetable_alloc_nolock(). > >> > >> As you cannot tolerate allocation failure and this is pretty much > >> permanent allocation (AFAIU) why don't you use a static allocation? > > > > Because of when bbl2_noabort is supported, that pages doesn't need to. > > If static alloc, that would be a waste in the system where bbl2_noabort > > is supported. > > > > When I tested, these extra pages are more than 40 in my FVP. > > So, it would be better dynamic allocation and I think since it's quite a > > early time, it's probably not failed that's why former code runs as it > > is. > > The required allocation size is also a function of the size of the installed RAM > so a static worst case allocation would consume all the RAM on small systems. Understood. But is it possible to pre-allocate early on so that the allocation itself doesn't have to happen from a constrained context. -- Michal Hocko SUSE Labs