From: Dan Williams <dan.j.williams@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Barret Rhoden <brho@google.com>, X86 ML <x86@kernel.org>,
"Zhang," Yu C" <yu.c.zhang@intel.com>,
KVM list <kvm@vger.kernel.org>," rkrcmar@redhat.com,
linux-nvdimm <linux-nvdimm@lists.01.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
zwisler@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.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.
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next prev parent 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 [RFC PATCH] kvm: Use huge pages for DAX-backed files Barret Rhoden
2018-10-29 22:25 ` Dan Williams
[not found] ` <CAPcyv4gJUjuSKwy7i2wuKR=Vz-AkDrxnGya5qkg7XTFxuXbtzw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2018-10-30 0:28 ` Barret Rhoden
2018-10-30 3:10 ` Dan Williams
[not found] ` <CAPcyv4gQztHrJ3--rhU4ZpaZyyqdqE0=gx50CRArHKiXwfYC+A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
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
[not found] ` <876d5a71-8dda-4728-5329-4e169777ba4a-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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
[not found] ` <20181029210716.212159-1-brho-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
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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