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From: Dan Williams <dan.j.williams@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Barret Rhoden <brho@google.com>,
	Dave Jiang <dave.jiang@intel.com>,
	zwisler@kernel.org, Vishal L Verma <vishal.l.verma@intel.com>,
	rkrcmar@redhat.com, Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
	KVM list <kvm@vger.kernel.org>,
	"Zhang, Yu C" <yu.c.zhang@intel.com>,
	"Zhang, Yi Z" <yi.z.zhang@intel.com>
Subject: Re: [RFC PATCH] kvm: Use huge pages for DAX-backed files
Date: Wed, 31 Oct 2018 14:16:01 -0700	[thread overview]
Message-ID: <CAPcyv4hqOhCBvYjxY31kc+BD+MraCBtou=MogApp_5wpz3W6Cw@mail.gmail.com> (raw)
In-Reply-To: <e00c5f69-f4d7-859c-cbde-0392b0a5195c@redhat.com>

On Wed, Oct 31, 2018 at 1:52 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 29/10/2018 23:25, Dan Williams wrote:
> > I'm wondering if we're adding an explicit is_zone_device_page() check
> > in this path to determine the page mapping size if that can be a
> > replacement for the kvm_is_reserved_pfn() check. In other words, the
> > goal of fixing up PageReserved() was to preclude the need for DAX-page
> > special casing in KVM, but if we already need add some special casing
> > for page size determination, might as well bypass the
> > kvm_is_reserved_pfn() dependency as well.
>
> No, please don't.  The kvm_is_reserved_pfn() check is for correctness,
> the page-size check is for optimization.  In theory you could have a
> ZONE_DEVICE area that is smaller than 2MB and thus does not use huge pages.

To be clear, I was not suggesting that a ZONE_DEVICE check would be
sufficient to determine a 2MB page. I was suggesting that given there
is a debate about removing the "reserved" designation for dax pages
that debate is moot if kvm is going to add interrogation code to
figure out the size of dax mappings.

  reply	other threads:[~2018-10-31 21:16 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-29 21:07 Barret Rhoden
2018-10-29 22:25 ` Dan Williams
2018-10-30  0:28   ` Barret Rhoden
2018-10-30  3:10     ` Dan Williams
2018-10-30 19:45       ` Barret Rhoden
2018-10-31  8:49         ` Paolo Bonzini
2018-11-02 20:32           ` Barret Rhoden
2018-11-06 10:19             ` Paolo Bonzini
2018-11-06 16:22               ` Barret Rhoden
2018-10-31  3:05       ` Yu Zhang
2018-10-31  8:52   ` Paolo Bonzini
2018-10-31 21:16     ` Dan Williams [this message]
2018-11-06 10:22       ` Paolo Bonzini
2018-11-06 21:05 ` Barret Rhoden
2018-11-06 21:16   ` Paolo Bonzini
2018-11-06 21:17     ` Barret Rhoden

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