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Mon, 4 Dec 2023 12:01:26 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id BB67E8B770; Mon, 4 Dec 2023 12:01:26 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id ugshGxlMuVrf; Mon, 4 Dec 2023 12:01:26 +0100 (CET) Received: from [172.25.230.108] (unknown [172.25.230.108]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 021778B763; Mon, 4 Dec 2023 12:01:25 +0100 (CET) Message-ID: <0d8c1623-8ab5-4d60-9989-1a7f712f40cd@csgroup.eu> Date: Mon, 4 Dec 2023 12:01:25 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 01/14] mm: Batch-copy PTE ranges during fork() Content-Language: fr-FR To: Andrew Morton , Ryan Roberts Cc: Catalin Marinas , Will Deacon , Ard Biesheuvel , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Zenghui Yu , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Anshuman Khandual , Matthew Wilcox , Yu Zhao , Mark Rutland , David Hildenbrand , Kefeng Wang , John Hubbard , Zi Yan , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20231115163018.1303287-1-ryan.roberts@arm.com> <20231115163018.1303287-2-ryan.roberts@arm.com> <20231115133743.674690dc78041768b79fadd9@linux-foundation.org> From: Christophe Leroy In-Reply-To: <20231115133743.674690dc78041768b79fadd9@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 7B3B0C0023 X-Stat-Signature: zeam8o4iy8qrgtegh361z3au4fhdb5m6 X-HE-Tag: 1701687689-612581 X-HE-Meta: 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 yu5HdLIg QMHxp3nnY/4ub9oAivtzlbMq2XKD9TSpMNJx+2pb36g8oTwbKEDmolkt3fUcagSeCWm7Q0D3DsftUj+lm0SHswaUv9iOHm6h2FRtRSoph5LMMDkOmi/IJwfuoJSIXIRuLLNY+AA3wD0N7ounV38SrZ0Cw6cdXyeXsKhkJVSSXPhqOha7qG6uau57mpU+6CFlyfq6IwJDrd1OHC6b2R8Mv7RH6rjr3cv3bWlaUUEuP/avRsDkWv+NQhfcDPm7H0NLhsTqGysctumqC3ioacKrGx2W3uL4TgzVLQw6SUP/C9xxWkoFITJ+XSSxAfMW/QfuODw6d 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: Le 15/11/2023 à 22:37, Andrew Morton a écrit : > On Wed, 15 Nov 2023 16:30:05 +0000 Ryan Roberts wrote: > >> However, the primary motivation for this change is to reduce the number >> of tlb maintenance operations that the arm64 backend has to perform >> during fork > > Do you have a feeling for how much performance improved due to this? > > Are there other architectures which might similarly benefit? By > implementing ptep_set_wrprotects(), it appears. If so, what sort of > gains might they see? > I think powerpc 8xx would benefit. We have 16k hugepages which are implemented with 4 identical PTE which have the _PAGE_SPS bit set. _PAGE_SPS says it is a 16k page. We have 512k hugepages which are implemented with 128 identical PTE which have _PAGE_HUGE bit set. _PAGE_HUGE tells it is a 512k page. FWIW, PMD size is 4M and there is no 4M page size so no way to implement leaf PMD huge pages. Christophe