linux-kernel - Re: [PATCH 3/4] writeback: nr_dirtied and nr

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Date:	Sun, 5 Sep 2010 22:17:15 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Michael Rubin <mrubin@...gle.com>,
	"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>,
	"david@...morbit.com" <david@...morbit.com>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"npiggin@...nel.dk" <npiggin@...nel.dk>, "hch@....de" <hch@....de>,
	"axboe@...nel.dk" <axboe@...nel.dk>
Subject: Re: [PATCH 3/4] writeback: nr_dirtied and nr_cleaned in
 /proc/vmstat

On Tue, Aug 31, 2010 at 03:48:25PM +0800, Wu Fengguang wrote:
> > > The output format is quite different from /proc/vmstat.
> > > Do we really need to "Node X", ":" and "times" decorations?
> > 
> > Node X is based on the meminfo file but I agree it's redundant information.
> 
> Thanks. In the same directory you can find a different style example
> /sys/devices/system/node/node0/numastat :) If ever the file was named
> vmstat! In the other hand, shall we put the numbers there? I'm confused..

With wider use of NUMA, I'm expecting more interests to put
/proc/vmstat items into /sys/devices/system/node/node0/.

What shall we do then? There are several possible options:
- just put the /proc/vmstat items into nodeX/numastat
- create nodeX/vmstat and make numastat a symlink to vmstat
- create nodeX/vmstat and remove numastat in future

Any suggestions?

> > > And the "_PAGES" in NR_FILE_PAGES_DIRTIED looks redundant to
> > > the "_page" in node_page_state(). It's a bit long to be a pleasant
> > > name. NR_FILE_DIRTIED/NR_CLEANED looks nicer.
> > 
> > Yeah. Will fix.
> 
> Thanks. This is kind of nitpick, however here is another name by
> Jan Kara: BDI_WRITTEN. BDI_WRITTEN may not be a lot better than
> BDI_CLEANED, but here is a patch based on Jan's code. I'm cooking
> more patches that make use of this per-bdi counter to estimate the
> bdi's write bandwidth, and to further decide the optimal (large)
> writeback chunk size as well as to do IO-less balance_dirty_pages().
> 
> Basically BDI_WRITTEN and NR_CLEANED are accounting for the same
> thing in different dimensions. So it would be good if we can use
> the same naming scheme to avoid confusing users: either to use
> BDI_WRITTEN and NR_WRITTEN, or use BDI_CLEANED and NR_CLEANED.
> What's your opinion?

I tend to prefer *_WRITTEN now.
- *_WRITTEN reminds the users about IO, *_CLEANED is less so obvious.
- *_CLEANED seems to be paired with NR_DIRTIED, this could be
  misleading to the users. The fact is, dirty pages may either be
  written to disk, or dropped (by truncate).

Thanks,
Fengguang
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