linux-kernel - Re: [PATCH v1 9/9] mm/memory: optimize unmap/zap with PTE-mapped THP

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Message-ID: <2375481c-9d61-4f06-9f96-232f25b0e49b@intel.com>
Date: Wed, 31 Jan 2024 10:30:00 +0800
From: Yin Fengwei <fengwei.yin@...el.com>
To: David Hildenbrand <david@...hat.com>, <linux-kernel@...r.kernel.org>
CC: <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, "Matthew
 Wilcox" <willy@...radead.org>, Ryan Roberts <ryan.roberts@....com>, "Catalin
 Marinas" <catalin.marinas@....com>, Will Deacon <will@...nel.org>, "Aneesh
 Kumar K.V" <aneesh.kumar@...ux.ibm.com>, Nick Piggin <npiggin@...il.com>,
	Peter Zijlstra <peterz@...radead.org>, Michael Ellerman <mpe@...erman.id.au>,
	Christophe Leroy <christophe.leroy@...roup.eu>, "Naveen N. Rao"
	<naveen.n.rao@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>, "Vasily
 Gorbik" <gor@...ux.ibm.com>, Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>, Sven Schnelle
	<svens@...ux.ibm.com>, Arnd Bergmann <arnd@...db.de>,
	<linux-arch@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	<linux-s390@...r.kernel.org>
Subject: Re: [PATCH v1 9/9] mm/memory: optimize unmap/zap with PTE-mapped THP



On 1/29/24 22:32, David Hildenbrand wrote:
> +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);
I am wondering whether it's worthy to move the pte_mkdirty() and pte_mkyoung()
out of the loop and just do it one time if needed. The worst case is that they
are called nr - 1 time. Or it's just too micro?


Regards
Yin, Fengwei

> +	}
> +	return pte;
> +}