linux-kernel - Re: [PATCH v3 5/9] x86/mm/tlb: Privatize cpu

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Date:   Fri, 19 Jul 2019 11:38:07 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Nadav Amit <namit@...are.com>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v3 5/9] x86/mm/tlb: Privatize cpu_tlbstate

On 7/18/19 5:58 PM, Nadav Amit wrote:
> +struct tlb_state_shared {
> +	/*
> +	 * We can be in one of several states:
> +	 *
> +	 *  - Actively using an mm.  Our CPU's bit will be set in
> +	 *    mm_cpumask(loaded_mm) and is_lazy == false;
> +	 *
> +	 *  - Not using a real mm.  loaded_mm == &init_mm.  Our CPU's bit
> +	 *    will not be set in mm_cpumask(&init_mm) and is_lazy == false.
> +	 *
> +	 *  - Lazily using a real mm.  loaded_mm != &init_mm, our bit
> +	 *    is set in mm_cpumask(loaded_mm), but is_lazy == true.
> +	 *    We're heuristically guessing that the CR3 load we
> +	 *    skipped more than makes up for the overhead added by
> +	 *    lazy mode.
> +	 */
> +	bool is_lazy;
> +};
> +DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_state_shared, cpu_tlbstate_shared);

Could we get a comment about what "shared" means and why we need shared
state?

Should we change 'tlb_state' to 'tlb_state_private'?