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X-IronPort-AV: E=McAfee;i="6600,9927,10879"; a="474479541" X-IronPort-AV: E=Sophos;i="6.03,265,1694761200"; d="scan'208";a="474479541" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Oct 2023 01:35:23 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10879"; a="795488444" X-IronPort-AV: E=Sophos;i="6.03,265,1694761200"; d="scan'208";a="795488444" Received: from xiaoyaol-hp-g830.ccr.corp.intel.com (HELO [10.93.9.145]) ([10.93.9.145]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Oct 2023 01:35:11 -0700 Message-ID: <7c0844d8-6f97-4904-a140-abeabeb552c1@intel.com> Date: Tue, 31 Oct 2023 16:35:08 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v13 17/35] KVM: Add transparent hugepage support for dedicated guest memory Content-Language: en-US To: Sean Christopherson , Paolo Bonzini , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Viro , Christian Brauner , "Matthew Wilcox (Oracle)" , Andrew Morton Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Xu Yilun , Chao Peng , Fuad Tabba , Jarkko Sakkinen , Anish Moorthy , David Matlack , Yu Zhang , Isaku Yamahata , =?UTF-8?B?TWlja2HDq2wgU2FsYcO8?= =?UTF-8?Q?n?= , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata , "Kirill A . Shutemov" References: <20231027182217.3615211-1-seanjc@google.com> <20231027182217.3615211-18-seanjc@google.com> From: Xiaoyao Li In-Reply-To: <20231027182217.3615211-18-seanjc@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: F23DF40015 X-Stat-Signature: fn5u458ntdahma5q5c5w7p9u997t61se X-HE-Tag: 1698741324-11550 X-HE-Meta: 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 2gqGJTUc ocXqcpQ22NIRMVYTpJOvPXbf238zk0h/L8/s1EQ9+KzldFUjS+ibREitlSq1esSMkPqYcDh7NlTQ3Q2K3KkMy2OZThofkbRSNbwa0GwIcBZ3BdmhPLFu2QmKKdF+xTGAcFwMbdYII8NNbu/u5mAYrax8+7fu0t5Er4TFBVOW5h7uK03Y7xE6wSKIGLBk5HCga0nT1vlo6okchxVn0VSsOs30+v4642gbevanS4y/GXmWb/UXXI7laeQSAKNU+suVfsb+v 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 10/28/2023 2:21 AM, Sean Christopherson wrote: > Extended guest_memfd to allow backing guest memory with transparent > hugepages. Require userspace to opt-in via a flag even though there's no > known/anticipated use case for forcing small pages as THP is optional, > i.e. to avoid ending up in a situation where userspace is unaware that > KVM can't provide hugepages. Personally, it seems not so "transparent" if requiring userspace to opt-in. People need to 1) check if the kernel built with TRANSPARENT_HUGEPAGE support, or check is the sysfs of transparent hugepage exists; 2)get the maximum support hugepage size 3) ensure the size satisfies the alignment; before opt-in it. Even simpler, userspace can blindly try to create guest memfd with transparent hugapage flag. If getting error, fallback to create without the transparent hugepage flag. However, it doesn't look transparent to me.