linux-kernel - Re: [RFC PATCH] kvm: Use huge pages for DAX-backed files

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Message-ID: <20181106112243.6fabdb0f@brho.roam.corp.google.com>
Date:   Tue, 6 Nov 2018 11:22:43 -0500
From:   Barret Rhoden <brho@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>, zwisler@...nel.org,
        Vishal L Verma <vishal.l.verma@...el.com>,
        rkrcmar@...hat.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        KVM list <kvm@...r.kernel.org>,
        "Zhang, Yu C" <yu.c.zhang@...el.com>,
        "Zhang, Yi Z" <yi.z.zhang@...el.com>
Subject: Re: [RFC PATCH] kvm: Use huge pages for DAX-backed files

On 2018-11-06 at 11:19 Paolo Bonzini <pbonzini@...hat.com> wrote:
> > 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.

You're right on that, I had it backwards.  The other DAX work is making
it so that DAX pages are not reserved, so the only extra '!' was in my
head.  

Thanks,

Barret