linux-kernel - Re: [RFC PATCH 08/21] KVM: TDX: Increase/decrease folio ref for huge pages

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Message-ID: <diqzms964lgu.fsf@ackerleytng-ctop.c.googlers.com>
Date: Mon, 14 Jul 2025 12:32:33 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: Vishal Annapurve <vannapurve@...gle.com>, "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, 
	"quic_eberman@...cinc.com" <quic_eberman@...cinc.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>, 
	"Shutemov, Kirill" <kirill.shutemov@...el.com>, "Hansen, Dave" <dave.hansen@...el.com>, 
	"david@...hat.com" <david@...hat.com>, "thomas.lendacky@....com" <thomas.lendacky@....com>, 
	"vbabka@...e.cz" <vbabka@...e.cz>, "tabba@...gle.com" <tabba@...gle.com>, "Du, Fan" <fan.du@...el.com>, 
	"michael.roth@....com" <michael.roth@....com>, "seanjc@...gle.com" <seanjc@...gle.com>, 
	"binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>, "Peng, Chao P" <chao.p.peng@...el.com>, 
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Yamahata, Isaku" <isaku.yamahata@...el.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Weiny, Ira" <ira.weiny@...el.com>, 
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "Li, Zhiquan1" <zhiquan1.li@...el.com>, 
	"jroedel@...e.de" <jroedel@...e.de>, "Miao, Jun" <jun.miao@...el.com>, 
	"pgonda@...gle.com" <pgonda@...gle.com>, "x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC PATCH 08/21] KVM: TDX: Increase/decrease folio ref for huge pages

Yan Zhao <yan.y.zhao@...el.com> writes:

> On Wed, Jul 02, 2025 at 11:43:23AM -0700, Ackerley Tng wrote:
>> >> vmemmap-optimized folios. Setting a page flag on a vmemmap-optimized
>> >> folio will be setting the flag on a few pages.
>> > BTW, I have a concern regarding to the overhead vmemmap-optimization.
>> >
>> > In my system,
>> > with hugetlb_free_vmemmap=false, the TD boot time is around 30s;
>> > with hugetlb_free_vmemmap=true, the TD boot time is around 1m20s;
>> 
>> I'm aware of this, was investigating this for something similar
>> internally. In your system and test, were you working with 1G pages, or
>> 2M pages?
> 2M pages. 

Thanks for letting me know. I'll look more into this. I'm currently also
working on some optimizations, hope this will get addressed.