linux-kernel - Re: [PATCH v3 2/4] mm/tlbbatch: Introduce arch_tlbbatch_should

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Message-ID: <0dc19773-81f7-84c2-2bc7-7d8d987b24b7@huawei.com>
Date:   Wed, 24 Aug 2022 17:40:06 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Yicong Yang <yangyicong@...wei.com>, <akpm@...ux-foundation.org>,
        <linux-mm@...ck.org>, <linux-arm-kernel@...ts.infradead.org>,
        <x86@...nel.org>, <catalin.marinas@....com>, <will@...nel.org>,
        <linux-doc@...r.kernel.org>
CC:     <corbet@....net>, <peterz@...radead.org>, <arnd@...db.de>,
        <linux-kernel@...r.kernel.org>, <darren@...amperecomputing.com>,
        <yangyicong@...ilicon.com>, <huzhanyuan@...o.com>,
        <lipeifeng@...o.com>, <zhangshiming@...o.com>, <guojian@...o.com>,
        <realmz6@...il.com>, <linux-mips@...r.kernel.org>,
        <openrisc@...ts.librecores.org>, <linuxppc-dev@...ts.ozlabs.org>,
        <linux-riscv@...ts.infradead.org>, <linux-s390@...r.kernel.org>,
        Barry Song <21cnbao@...il.com>, <xhao@...ux.alibaba.com>,
        <prime.zeng@...ilicon.com>, <anshuman.khandual@....com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3 2/4] mm/tlbbatch: Introduce
 arch_tlbbatch_should_defer()


On 2022/8/22 16:21, Yicong Yang wrote:
> From: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
>
> The entire scheme of deferred TLB flush in reclaim path rests on the
> fact that the cost to refill TLB entries is less than flushing out
> individual entries by sending IPI to remote CPUs. But architecture
> can have different ways to evaluate that. Hence apart from checking
> TTU_BATCH_FLUSH in the TTU flags, rest of the decision should be
> architecture specific.
>
> Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
> [https://lore.kernel.org/linuxppc-dev/20171101101735.2318-2-khandual@linux.vnet.ibm.com/]
> Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
> [Rebase and fix incorrect return value type]

Reviewed-by: Kefeng Wang <wangkefeng.wang@...wei.com>

> ---
>   arch/x86/include/asm/tlbflush.h | 12 ++++++++++++
>   mm/rmap.c                       |  9 +--------
>   2 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index cda3118f3b27..8a497d902c16 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -240,6 +240,18 @@ static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long a)
>   	flush_tlb_mm_range(vma->vm_mm, a, a + PAGE_SIZE, PAGE_SHIFT, false);
>   }
>   
> +static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm)
> +{
> +	bool should_defer = false;
> +
> +	/* If remote CPUs need to be flushed then defer batch the flush */
> +	if (cpumask_any_but(mm_cpumask(mm), get_cpu()) < nr_cpu_ids)
> +		should_defer = true;
> +	put_cpu();
> +
> +	return should_defer;
> +}
> +
>   static inline u64 inc_mm_tlb_gen(struct mm_struct *mm)
>   {
>   	/*
> diff --git a/mm/rmap.c b/mm/rmap.c
> index edc06c52bc82..a17a004550c6 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -687,17 +687,10 @@ static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
>    */
>   static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
>   {
> -	bool should_defer = false;
> -
>   	if (!(flags & TTU_BATCH_FLUSH))
>   		return false;
>   
> -	/* If remote CPUs need to be flushed then defer batch the flush */
> -	if (cpumask_any_but(mm_cpumask(mm), get_cpu()) < nr_cpu_ids)
> -		should_defer = true;
> -	put_cpu();
> -
> -	return should_defer;
> +	return arch_tlbbatch_should_defer(mm);
>   }
>   
>   /*