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Shutemov" , Yin Fengwei , David Hildenbrand , Yu Zhao , Catalin Marinas , Will Deacon , Anshuman Khandual , Yang Shi , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 4/5] mm: FLEXIBLE_THP for improved performance References: <20230703135330.1865927-1-ryan.roberts@arm.com> <20230703135330.1865927-5-ryan.roberts@arm.com> Date: Fri, 07 Jul 2023 16:01:45 +0800 In-Reply-To: <20230703135330.1865927-5-ryan.roberts@arm.com> (Ryan Roberts's message of "Mon, 3 Jul 2023 14:53:29 +0100") Message-ID: <87edlkgnfa.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspamd-Queue-Id: 5020540006 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: ugscec7qw7rjshaaksfk9ih71rm7o145 X-HE-Tag: 1688717020-112917 X-HE-Meta: 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 gOy22T50 srOy9AQxShzWcW9fecmY6VyzfGd8qc7FY2XwK29z2e5IYszgWTr1ogpG3VrTUy6QW8C4oD3sT/NaO8G4d497zLKMoTFamqOPJZh6AikbgC16L4IkIiqytWZyB8XuxwdC52fVp9msOvyCC2jnOjN3a2gtQfkKOjmEQEedyLMoO9eQnTCRHuL9nAM29g3wfXUvmvPjI/521pzCIPhlLi2wg3K36IwD8q8tnLGmImFpwPEtAKwdJU97ZTZ+jR/J/11ZPPeyw 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: Ryan Roberts writes: > Introduce FLEXIBLE_THP feature, which allows anonymous memory to be > allocated in large folios of a specified order. All pages of the large > folio are pte-mapped during the same page fault, significantly reducing > the number of page faults. The number of per-page operations (e.g. ref > counting, rmap management lru list management) are also significantly > reduced since those ops now become per-folio. I likes the idea to share as much code as possible between large (anonymous) folio and THP. Finally, THP becomes just a special kind of large folio. Although we can use smaller page order for FLEXIBLE_THP, it's hard to avoid internal fragmentation completely. So, I think that finally we will need to provide a mechanism for the users to opt out, e.g., something like "always madvise never" via /sys/kernel/mm/transparent_hugepage/enabled. I'm not sure whether it's a good idea to reuse the existing interface of THP. Best Regards, Huang, Ying