linux-kernel - Re: [PATCH 5/7] powerpc/mm: support nested lazy

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Message-ID: <074ff6ab-5868-4fde-b5bb-9e17632ad817-agordeev@linux.ibm.com>
Date: Fri, 5 Sep 2025 17:52:43 +0200
From: Alexander Gordeev <agordeev@...ux.ibm.com>
To: Kevin Brodsky <kevin.brodsky@....com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andreas Larsson <andreas@...sler.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jann Horn <jannh@...gle.com>, Juergen Gross <jgross@...e.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>, Michal Hocko <mhocko@...e.com>,
        Mike Rapoport <rppt@...nel.org>, Nicholas Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ryan Roberts <ryan.roberts@....com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 5/7] powerpc/mm: support nested lazy_mmu sections

On Thu, Sep 04, 2025 at 01:57:34PM +0100, Kevin Brodsky wrote:
...
>  static inline lazy_mmu_state_t arch_enter_lazy_mmu_mode(void)
>  {
>  	struct ppc64_tlb_batch *batch;
> +	int lazy_mmu_nested;
>  
>  	if (radix_enabled())
>  		return LAZY_MMU_DEFAULT;
> @@ -39,9 +40,14 @@ static inline lazy_mmu_state_t arch_enter_lazy_mmu_mode(void)
>  	 */
>  	preempt_disable();
>  	batch = this_cpu_ptr(&ppc64_tlb_batch);
> -	batch->active = 1;
> +	lazy_mmu_nested = batch->active;
>  
> -	return LAZY_MMU_DEFAULT;
> +	if (!lazy_mmu_nested) {

Why not just?

	if (!batch->active) {

> +		batch->active = 1;
> +		return LAZY_MMU_DEFAULT;
> +	} else {
> +		return LAZY_MMU_NESTED;
> +	}
>  }
>  
>  static inline void arch_leave_lazy_mmu_mode(lazy_mmu_state_t state)
> @@ -54,7 +60,10 @@ static inline void arch_leave_lazy_mmu_mode(lazy_mmu_state_t state)
>  
>  	if (batch->index)
>  		__flush_tlb_pending(batch);
> -	batch->active = 0;
> +
> +	if (state != LAZY_MMU_NESTED)
> +		batch->active = 0;
> +
>  	preempt_enable();
>  }

Thanks!