linux-kernel - Re: [PATCH v3 04/11] x86/mm: Give each mm TLB flush generation a unique ID

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Message-ID: <20170621174320.gouuexwzoau6pjnj@pd.tnic>
Date:   Wed, 21 Jun 2017 19:43:20 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Rik van Riel <riel@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3 04/11] x86/mm: Give each mm TLB flush generation a
 unique ID

On Tue, Jun 20, 2017 at 10:22:10PM -0700, Andy Lutomirski wrote:
> - * The x86 doesn't have a mmu context, but
> - * we put the segment information here.
> + * x86 has arch-specific MMU state beyond what lives in mm_struct.
>   */
>  typedef struct {
> +	/*
> +	 * ctx_id uniquely identifies this mm_struct.  A ctx_id will never
> +	 * be reused, and zero is not a valid ctx_id.
> +	 */
> +	u64 ctx_id;
> +
> +	/*
> +	 * Any code that needs to do any sort of TLB flushing for this
> +	 * mm will first make its changes to the page tables, then
> +	 * increment tlb_gen, then flush.  This lets the low-level
> +	 * flushing code keep track of what needs flushing.
> +	 *
> +	 * This is not used on Xen PV.
> +	 */
> +	atomic64_t tlb_gen;

Btw, can this just be a 4-byte int instead? I.e., simply atomic_t. I
mean, it should be enough for all the TLB generations in flight, no?

-- 
Regards/Gruss,
    Boris.

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