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

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Message-ID: <bd157a11-8e6b-5f44-4d91-d99adb9f8686@intel.com>
Date:   Mon, 25 Jan 2021 17:04:00 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tejun Heo <tj@...nel.org>
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

On 1/25/21 4:53 PM, Tejun Heo wrote:
>> 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.

Which part?  Large production environments don't trust data from
debugfs?  Or don't trust it if it might have been reset?

You could stick the "reset" switch in debugfs, and dump something out in
dmesg like we do for /proc/sys/vm/drop_caches so it's not a surprise
that it happened.

BTW, counts of *events* don't really belong in meminfo.  These really do
belong in /proc/vmstat if anything.