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Subject: Re: [RFC PATCH] kvm: Use huge pages for DAX-backed files
To:     Barret Rhoden <brho@google.com>,
        Dan Williams <dan.j.williams@intel.com>
Cc:     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>
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From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Tue, 6 Nov 2018 11:19:18 +0100
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On 02/11/2018 21:32, Barret Rhoden wrote:
> One of the other things I noticed was some places in KVM make a
> distinction between kvm_is_reserved_pfn and PageReserved:
> 
> void kvm_set_pfn_dirty(kvm_pfn_t pfn)
> {
>         if (!kvm_is_reserved_pfn(pfn)) {
>                 struct page *page = pfn_to_page(pfn);
> 
>                 if (!PageReserved(page))
>                         SetPageDirty(page);
>         }
> }
> 
> I think we want to SetPageDirty for DAX, so making PageReserved be true
> for DAX seems like the way to go, or we'll need more KVM-specific
> changes.  Apologies is this was discussed in the previous thread on this
> topic and is redundant.

Isn't it the opposite?  We want SetPageDirty, so PageReserved must _not_
be true.

Paolo