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Date: Tue, 30 Jan 2024 10:08:53 +0100
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Subject: Re: [PATCH v1 9/9] mm/memory: optimize unmap/zap with PTE-mapped THP
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To: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
 Matthew Wilcox <willy@infradead.org>, Ryan Roberts <ryan.roberts@arm.com>,
 Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>,
 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
 Nick Piggin <npiggin@gmail.com>, Peter Zijlstra <peterz@infradead.org>,
 Michael Ellerman <mpe@ellerman.id.au>,
 Christophe Leroy <christophe.leroy@csgroup.eu>,
 "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
 Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>,
 Alexander Gordeev <agordeev@linux.ibm.com>,
 Christian Borntraeger <borntraeger@linux.ibm.com>,
 Sven Schnelle <svens@linux.ibm.com>, Arnd Bergmann <arnd@arndb.de>,
 linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
 linux-s390@vger.kernel.org
References: <20240129143221.263763-1-david@redhat.com>
 <20240129143221.263763-10-david@redhat.com>
From: David Hildenbrand <david@redhat.com>
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Re-reading the docs myself:

> +#ifndef get_and_clear_full_ptes
> +/**
> + * get_and_clear_full_ptes - Clear PTEs that map consecutive pages of the same
> + *			     folio, collecting dirty/accessed bits.
> + * @mm: Address space the pages are mapped into.
> + * @addr: Address the first page is mapped at.
> + * @ptep: Page table pointer for the first entry.
> + * @nr: Number of entries to clear.
> + * @full: Whether we are clearing a full mm.
> + *
> + * May be overridden by the architecture; otherwise, implemented as a simple
> + * loop over ptep_get_and_clear_full(), merging dirty/accessed bits into
> + * returned PTE.

"into the"

> + *
> + * Note that PTE bits in the PTE range besides the PFN can differ. For example,
> + * some PTEs might be write-protected.
> + *
> + * Context: The caller holds the page table lock.  The PTEs map consecutive
> + * pages that belong to the same folio.  The PTEs are all in the same PMD.
> + */
> +static inline pte_t get_and_clear_full_ptes(struct mm_struct *mm,
> +		unsigned long addr, pte_t *ptep, unsigned int nr, int full)
> +{
> +	pte_t pte, tmp_pte;
> +
> +	pte = ptep_get_and_clear_full(mm, addr, ptep, full);
> +	while (--nr) {
> +		ptep++;
> +		addr += PAGE_SIZE;
> +		tmp_pte = ptep_get_and_clear_full(mm, addr, ptep, full);
> +		if (pte_dirty(tmp_pte))
> +			pte = pte_mkdirty(pte);
> +		if (pte_young(tmp_pte))
> +			pte = pte_mkyoung(pte);
> +	}
> +	return pte;
> +}
> +#endif
> +
> +#ifndef clear_full_ptes
> +/**
> + * clear_full_ptes - Clear PTEs that map consecutive pages of the same folio.
> + * @mm: Address space the pages are mapped into.
> + * @addr: Address the first page is mapped at.
> + * @ptep: Page table pointer for the first entry.
> + * @nr: Number of entries to clear.
> + * @full: Whether we are clearing a full mm.

Something went missing:

May be overridden by the architecture; otherwise, implemented as a 
simple loop over ptep_get_and_clear_full().


-- 
Cheers,

David / dhildenb