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

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Message-ID: <876d5a71-8dda-4728-5329-4e169777ba4a@redhat.com>
Date:   Tue, 6 Nov 2018 11:19:18 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Barret Rhoden <brho@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     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 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