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

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Date:	Fri, 20 Aug 2010 16:51:38 -0700
From:	Michael Rubin <mrubin@...gle.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	"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 3/4] writeback: nr_dirtied and nr_entered_writeback in /proc/vmstat

On Fri, Aug 20, 2010 at 3:08 AM, Wu Fengguang <fengguang.wu@...el.com> wrote:
> How about the names nr_dirty_accumulated and nr_writeback_accumulated?
> It seems more consistent, for both the interface and code (see below).
> I'm not really sure though.

Those names don't seem to right to me.
I admit I like "nr_dirtied" and "nr_cleaned" that seems most
understood. These numbers also get very big pretty fast so I don't
think it's hard to infer.

>> In order to track the "cleaned" and "dirtied" counts we added two
>> vm_stat_items.  Per memory node stats have been added also. So we can
>> see per node granularity:
>>
>>    # cat /sys/devices/system/node/node20/writebackstat
>>    Node 20 pages_writeback: 0 times
>>    Node 20 pages_dirtied: 0 times
>
> I'd prefer the name "vmstat" over "writebackstat", and propose to
> migrate items from /proc/zoneinfo over time. zoneinfo is a terrible
> interface for scripting.

I like vmstat also. I can do that.

> Also, are there meaningful usage of per-node writeback stats?

For us yes. We use fake numa nodes to implement cgroup memory isolation.
This allows us to see what the writeback behaviour is like per cgroup.

> The numbers are naturally per-bdi ones instead. But if we plan to
> expose them for each bdi, this patch will need to be implemented
> vastly differently.

Currently I have no plans to do that.

mrubin
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