linux-kernel - Re: [PATCHv5 02/12] mm: Add support for unaccepted memory

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Date:   Fri, 6 May 2022 03:54:58 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     David Hildenbrand <david@...hat.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Varad Gautam <varad.gautam@...e.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Mike Rapoport <rppt@...nel.org>, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCHv5 02/12] mm: Add support for unaccepted memory

On Tue, May 03, 2022 at 10:21:03PM +0200, David Hildenbrand wrote:
> 
> >  
> > +/*
> > + * Page acceptance can be very slow. Do not call under critical locks.
> > + */
> > +static void accept_page(struct page *page, unsigned int order)
> > +{
> > +	phys_addr_t start = page_to_phys(page);
> > +	int i;
> > +
> > +	accept_memory(start, start + (PAGE_SIZE << order));
> > +
> > +	for (i = 0; i < (1 << order); i++) {
> > +		if (PageUnaccepted(page + i))
> > +			__ClearPageUnaccepted(page + i);
> > +	}
> > +}
> 
> What was the rationale of leaving PageUnaccepted() set on sub-pages when
> merging pages?
> 
> I'd just clear the flag when merging and avoid the loop here. You could
> even assert here that we don't have any PageUnaccepted() on tail pages.

Okay, fair enough. I will change the code.

-- 
 Kirill A. Shutemov