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Date:   Wed, 13 Apr 2022 17:39:20 +0300
From:   Mike Rapoport <rppt@kernel.org>
To:     David Hildenbrand <david@redhat.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>,
        Ard Biesheuvel <ardb@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Varad Gautam <varad.gautam@suse.com>,
        Dario Faggioli <dfaggioli@suse.com>,
        Brijesh Singh <brijesh.singh@amd.com>, x86@kernel.org,
        linux-mm@kvack.org, linux-coco@lists.linux.dev,
        linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [PATCHv4 1/8] mm: Add support for unaccepted memory
Message-ID: <YlbgmOwb9uXMt49l@kernel.org>
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On Wed, Apr 13, 2022 at 12:36:11PM +0200, David Hildenbrand wrote:
> On 12.04.22 18:08, Dave Hansen wrote:
> > On 4/12/22 01:15, David Hildenbrand wrote:
> > 
> > The other option might be to tie this all to DEFERRED_STRUCT_PAGE_INIT.
> >  Have the rule that everything that gets a 'struct page' must be
> > accepted.  If you want to do delayed acceptance, you do it via
> > DEFERRED_STRUCT_PAGE_INIT.
> 
> That could also be an option, yes. At least being able to chose would be
> good. But IIRC, DEFERRED_STRUCT_PAGE_INIT will still make the system get
> stuck during boot and wait until everything was accepted.

The deferred page init runs multithreaded, so guest with SMP will be stuck
for less time.
 
> I see the following variants:
> 
> 1) Slow boot; after boot, all memory is already accepted.
> 2) Fast boot; after boot, all memory will slowly but steadily get
>    accepted in the background. After a while, all memory is accepted and
>    can be signaled to user space.
> 3) Fast boot; after boot, memory gets accepted on demand. This is what
>    we have in this series.
> 
> I somehow don't quite like 3), but with deferred population in the
> hypervisor, it might just make sense.

IMHO, deferred population in hypervisor will be way more complex than this
series with similar "visible" performance.

-- 
Sincerely yours,
Mike.