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

From: David Hildenbrand <david@redhat.com>
To: "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>
Cc: 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>,
	Dave Hansen <dave.hansen@intel.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Mike Rapoport <rppt@kernel.org>,
	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: [PATCHv5 02/12] mm: Add support for unaccepted memory
Date: Tue, 3 May 2022 22:21:03 +0200	[thread overview]
Message-ID: <2bb92a84-18f4-d007-9465-fdc19f6f1c86@redhat.com> (raw)
In-Reply-To: <20220425033934.68551-3-kirill.shutemov@linux.intel.com>

>  
> +/*
> + * 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.

-- 
Thanks,

David / dhildenb