linux-kernel - Re: [PATCH] x86/mm: Tracking linear mapping split events since boot

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Message-ID: <YA9oD2djENLo4975@slm.duckdns.org>
Date:   Mon, 25 Jan 2021 19:53:35 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Saravanan D <saravanand@...look.com>, x86@...nel.org,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH] x86/mm: Tracking linear mapping split events since boot

Hello, Dave.

On Mon, Jan 25, 2021 at 04:47:42PM -0800, Dave Hansen wrote:
> The patch here does not actually separate out pre-boot from post-boot,
> so it's pretty hard to tell if the splits came from something like
> tracing which is totally unnecessary or they were the result of
> something at boot that we can't do anything about.

Ah, right, didn't know they also included splits during boot. It'd be a lot
more useful if they were counting post-boot splits.

> This would be a lot more useful if you could reset the counters.  Then
> just reset them from userspace at boot.  Adding read-write debugfs
> exports for these should be pretty trivial.

While this would work for hands-on cases, I'm a bit worried that this might
be more challenging to gain confidence in large production environments.

Thanks.

-- 
tejun