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From: Tejun Heo <tj@kernel.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Saravanan D <saravanand@outlook.com>,
	x86@kernel.org, dave.hansen@linux.intel.com, luto@kernel.org,
	peterz@infradead.org, linux-kernel@vger.kernel.org,
	kernel-team@fb.com
Subject: Re: [PATCH] x86/mm: Tracking linear mapping split events since boot
Date: Mon, 25 Jan 2021 20:17:07 -0500	[thread overview]
Message-ID: <YA9tk7Tnp2AEEcCU@slm.duckdns.org> (raw)
In-Reply-To: <bd157a11-8e6b-5f44-4d91-d99adb9f8686@intel.com>

Hello,

On Mon, Jan 25, 2021 at 05:04:00PM -0800, Dave Hansen wrote:
> Which part?  Large production environments don't trust data from
> debugfs?  Or don't trust it if it might have been reset?

When the last reset was. Not saying it's impossible or anything but in
general it's a lot better to have the counters to be monotonically
increasing with time/event stamped markers than the counters themselves
getting reset or modified in other ways because the ownership of a specific
counter might not be obvious to everyone and accidents and mistakes happen.

Note that the "time/event stamped markers" above don't need to and shouldn't
be in the kernel. It can be managed by whoever that wants to monitor a given
time period and there can be any number of them.

> 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.

Processing dmesgs can work too but isn't particularly reliable or scalable.

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

Oh yeah, I don't have a strong opinion on where the counters should go.

Thanks.

-- 
tejun

  reply	other threads:[~2021-01-26 10:30 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <BYAPR01MB40856478D5BE74CB6A7D5578CFBD9@BYAPR01MB4085.prod.exchangelabs.com>
2021-01-25 20:15 ` [PATCH] x86/mm: Tracking linear mapping split events since boot Dave Hansen
2021-01-25 20:32   ` Tejun Heo
2021-01-26  0:47     ` Dave Hansen
2021-01-26  0:53       ` Tejun Heo
2021-01-26  1:04         ` Dave Hansen
2021-01-26  1:17           ` Tejun Heo [this message]
2021-01-27 17:51           ` [PATCH V2] x86/mm: Tracking linear mapping split events Saravanan D
2021-01-27 21:03             ` Tejun Heo
2021-01-27 21:32               ` Dave Hansen
2021-01-27 21:36                 ` Tejun Heo
2021-01-27 21:42                   ` Saravanan D
2021-01-27 22:50                   ` [PATCH V3] " Saravanan D
2021-01-27 23:00                     ` Randy Dunlap
2021-01-27 23:56                       ` Saravanan D
2021-01-27 23:41                     ` Dave Hansen
2021-01-28  0:15                       ` Saravanan D
2021-01-28  4:35                       ` [PATCH V4] " Saravanan D
2021-01-28  4:51                         ` Matthew Wilcox
     [not found]                           ` <20210128104934.2916679-1-saravanand@fb.com>
2021-01-28 15:04                             ` [PATCH V5] " Matthew Wilcox
2021-01-28 19:49                               ` Saravanan D
2021-01-28 16:33                             ` Zi Yan
2021-01-28 16:41                               ` Dave Hansen
2021-01-28 16:56                                 ` Zi Yan
2021-01-28 16:59                               ` Song Liu
     [not found]                             ` <3aec2d10-f4c3-d07a-356f-6f1001679181@intel.com>
2021-01-28 21:20                               ` Saravanan D
     [not found]                                 ` <20210128233430.1460964-1-saravanand@fb.com>
2021-01-28 23:41                                   ` [PATCH V6] " Tejun Heo
2021-01-29 19:27                                   ` Johannes Weiner
2021-02-08 23:17                                     ` Saravanan D
2021-02-08 23:30                                   ` Dave Hansen

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