linux-kernel - Re: [patch V3 11/11] x86/mm/cpa: Avoid the 4k pages check completely

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Message-ID: <8b83d5e2-2374-1986-5fae-9e898eee1a7b@intel.com>
Date:   Fri, 21 Sep 2018 13:32:12 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
        Bin Yang <bin.yang@...el.com>,
        Mark Gross <mark.gross@...el.com>
Subject: Re: [patch V3 11/11] x86/mm/cpa: Avoid the 4k pages check completely

On 09/17/2018 07:29 AM, Thomas Gleixner wrote:
> +	 * There used to be a 4k wise evaluation trying really hard to
> +	 * preserve the large pages, but experimentation has shown, that this
> +	 * does not help at all. There might be corner cases which would
> +	 * preserve one large page occasionally, but it's really not worth the
> +	 * extra code and cycles for the common case.

My only concern with this is that if this goes bad, it will be silently
bad and we'll just have an unnecessarily fractured direct map.

But, writing code to go verify the page tables and make sure they're
sane is a task for another day.

Reviewed-by: Dave Hansen <dave.hansen@...el.com>