linux-kernel - Re: [PATCH v2] x86: enable RCU based table free

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Message-ID: <20170824143434.r7v3bjm3f32yvfg7@hirez.programming.kicks-ass.net>
Date:   Thu, 24 Aug 2017 16:34:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jork Loeser <Jork.Loeser@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v2] x86: enable RCU based table free

On Thu, Aug 24, 2017 at 11:22:58AM +0200, Vitaly Kuznetsov wrote:

> diff --git a/arch/x86/include/asm/tlb.h b/arch/x86/include/asm/tlb.h
> index c7797307fc2b..d43a7fcafee9 100644
> --- a/arch/x86/include/asm/tlb.h
> +++ b/arch/x86/include/asm/tlb.h
> @@ -15,4 +15,9 @@
>  
>  #include <asm-generic/tlb.h>
>  
> +static inline void __tlb_remove_table(void *table)
> +{
> +	free_page_and_swap_cache(table);
> +}

Most other archs have this in pgtable.h, only ARM* has it in tlb.h.

And should we put a comment on explaining _why_ we have RCU_TABLE_FREE
enabled?

>  #endif /* _ASM_X86_TLB_H */
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index 508a708eb9a6..218834a3e9ad 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -56,7 +56,7 @@ void ___pte_free_tlb(struct mmu_gather *tlb, struct page *pte)
>  {
>  	pgtable_page_dtor(pte);
>  	paravirt_release_pte(page_to_pfn(pte));
> -	tlb_remove_page(tlb, pte);
> +	tlb_remove_table(tlb, pte);
>  }
>  
>  #if CONFIG_PGTABLE_LEVELS > 2
> @@ -72,21 +72,21 @@ void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)
>  	tlb->need_flush_all = 1;
>  #endif
>  	pgtable_pmd_page_dtor(page);
> -	tlb_remove_page(tlb, page);
> +	tlb_remove_table(tlb, page);
>  }
>  
>  #if CONFIG_PGTABLE_LEVELS > 3
>  void ___pud_free_tlb(struct mmu_gather *tlb, pud_t *pud)
>  {
>  	paravirt_release_pud(__pa(pud) >> PAGE_SHIFT);
> -	tlb_remove_page(tlb, virt_to_page(pud));
> +	tlb_remove_table(tlb, virt_to_page(pud));
>  }
>  
>  #if CONFIG_PGTABLE_LEVELS > 4
>  void ___p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d)
>  {
>  	paravirt_release_p4d(__pa(p4d) >> PAGE_SHIFT);
> -	tlb_remove_page(tlb, virt_to_page(p4d));
> +	tlb_remove_table(tlb, virt_to_page(p4d));
>  }
>  #endif	/* CONFIG_PGTABLE_LEVELS > 4 */
>  #endif	/* CONFIG_PGTABLE_LEVELS > 3 */
> -- 
> 2.13.5
>