linux-kernel - Re: [PATCH 4/4] writeback: Reporting dirty thresholds in /proc/vmstat

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Date:	Tue, 24 Aug 2010 10:11:36 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Michael Rubin <mrubin@...gle.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"jack@...e.cz" <jack@...e.cz>, "riel@...hat.com" <riel@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"david@...morbit.com" <david@...morbit.com>,
	"npiggin@...nel.dk" <npiggin@...nel.dk>, "hch@....de" <hch@....de>,
	"axboe@...nel.dk" <axboe@...nel.dk>
Subject: Re: [PATCH 4/4] writeback: Reporting dirty thresholds in
 /proc/vmstat

> Right now we don't mount all of debugfs at boot time. We have not done
> the work to verify its safe in our environment. It's mostly a nit.

You work discreetly, that's a good thing. Note that most
sub-directories under debugfs can be turned off in kconfig.

> Also I was under the impression that debugfs was intended more for
> kernel devs while /proc and /sys was intended for application
> developers.

I guess the keyword here is "debugging/diagnosing". Think about
/debug/tracing. DirtyThresh seems like the same stuff.

> >> 3) Full system counters are easier to handle the juggling of removable
> >> storage where these numbers will appear and disappear due to being
> >> dynamic.
> 
> This is the biggie to me. The idea is to get a complete view of the
> system's writeback behaviour over time. With systems with hot plug
> devices, or many many drives collecting that view gets difficult.

Sorry for giving a wrong example. Hope this one is better:

$ cat /debug/bdi/default/stats
[...]
DirtyThresh:       1838904 kB
BackgroundThresh:   919452 kB
[...]

It's a trick to avoid messing with real devices :)

Thanks,
Fengguang
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