linux-kernel - Re: [PATCH] x86/mm/tlb: avoid reading mm_tlb

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Date:   Mon, 6 Jun 2022 08:29:49 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Nadav Amit <nadav.amit@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Nadav Amit <namit@...are.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org
Subject: Re: [PATCH] x86/mm/tlb: avoid reading mm_tlb_gen when possible

On 3/22/22 15:07, Nadav Amit wrote:
> +	if (f->new_tlb_gen <= local_tlb_gen) {
> +		/*
> +		 * We are already up to date in respect to f->new_tlb_gen.
> +		 * While the core might be still behind mm_tlb_gen, checking
> +		 * mm_tlb_gen unnecessarily would have negative caching effects
> +		 * so avoid it.
> +		 */
> +		return;
> +	}
> +

Nit: There's at least one "we" in here that needs to get fixed up.  I'll
plan to do that when I apply it, but a v2 with that fixed and Peter's
ack added might save me five minutes.