linux-kernel - Re: [PATCH v1 8/9] mm/mmu_gather: add tlb_remove_tlb

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Date: Tue, 30 Jan 2024 09:33:19 +0000
From: Ryan Roberts <ryan.roberts@....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>,
 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 8/9] mm/mmu_gather: add tlb_remove_tlb_entries()

On 29/01/2024 14:32, David Hildenbrand wrote:
> Let's add a helper that lets us batch-process multiple consecutive PTEs.
> 
> Note that the loop will get optimized out on all architectures except on
> powerpc. We have to add an early define of __tlb_remove_tlb_entry() on
> ppc to make the compiler happy (and avoid making tlb_remove_tlb_entries() a
> macro).
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Ryan Roberts <ryan.roberts@....com>

> ---
>  arch/powerpc/include/asm/tlb.h |  2 ++
>  include/asm-generic/tlb.h      | 20 ++++++++++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/tlb.h b/arch/powerpc/include/asm/tlb.h
> index b3de6102a907..1ca7d4c4b90d 100644
> --- a/arch/powerpc/include/asm/tlb.h
> +++ b/arch/powerpc/include/asm/tlb.h
> @@ -19,6 +19,8 @@
>  
>  #include <linux/pagemap.h>
>  
> +static inline void __tlb_remove_tlb_entry(struct mmu_gather *tlb, pte_t *ptep,
> +					  unsigned long address);
>  #define __tlb_remove_tlb_entry	__tlb_remove_tlb_entry
>  
>  #define tlb_flush tlb_flush
> diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
> index 428c3f93addc..bd00dd238b79 100644
> --- a/include/asm-generic/tlb.h
> +++ b/include/asm-generic/tlb.h
> @@ -616,6 +616,26 @@ static inline void tlb_flush_p4d_range(struct mmu_gather *tlb,
>  		__tlb_remove_tlb_entry(tlb, ptep, address);	\
>  	} while (0)
>  
> +/**
> + * tlb_remove_tlb_entries - remember unmapping of multiple consecutive ptes for
> + *			    later tlb invalidation.
> + *
> + * Similar to tlb_remove_tlb_entry(), but remember unmapping of multiple
> + * consecutive ptes instead of only a single one.
> + */
> +static inline void tlb_remove_tlb_entries(struct mmu_gather *tlb,
> +		pte_t *ptep, unsigned int nr, unsigned long address)
> +{
> +	tlb_flush_pte_range(tlb, address, PAGE_SIZE * nr);
> +	for (;;) {
> +		__tlb_remove_tlb_entry(tlb, ptep, address);
> +		if (--nr == 0)
> +			break;
> +		ptep++;
> +		address += PAGE_SIZE;
> +	}
> +}
> +
>  #define tlb_remove_huge_tlb_entry(h, tlb, ptep, address)	\
>  	do {							\
>  		unsigned long _sz = huge_page_size(h);		\