Date: Fri, 20 Aug 2010 14:54:29 +0800
From: Wu Fengguang <fengguang.wu@intel.com>
To: Michael Rubin <mrubin@google.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, jack@suse.cz, riel@redhat.com,
        akpm@linux-foundation.org, david@fromorbit.com, npiggin@suse.de,
        hch@lst.de, axboe@kernel.dk
Subject: Re: [PATCH 2/3] writeback: Adding pages_dirtied and
 pages_entered_writeback
Message-ID: <20100820065429.GA6828@localhost>
References: <1282251447-16937-1-git-send-email-mrubin@google.com>
 <1282251447-16937-3-git-send-email-mrubin@google.com>
 <20100820025111.GB5502@localhost>
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Sorry, here is the mentioned vmmon source file.

The full ext3-tools package is here:

        http://userweb.kernel.org/~akpm/stuff/ext3-tools.tar.gz

Thanks,
Fengguang

On Fri, Aug 20, 2010 at 10:51:11AM +0800, Wu Fengguang wrote:
> On Thu, Aug 19, 2010 at 01:57:26PM -0700, Michael Rubin wrote:
> > To help developers and applications gain visibility into writeback
> > behaviour adding four read only sysctl files into /proc/sys/vm.
> > These files allow user apps to understand writeback behaviour over time
> > and learn how it is impacting their performance.
> > 
> >    # cat /proc/sys/vm/pages_dirtied
> >    3747
> >    # cat /proc/sys/vm/pages_entered_writeback
> >    3618
> 
> As Rik said, /proc/sys is not a suitable place.
> 
> Frankly speaking I've worked on writeback for years and never felt
> the need to add these counters. What I often do is:
> 
> $ vmmon -d 1 nr_writeback nr_dirty nr_unstable
> 
>      nr_writeback         nr_dirty      nr_unstable
>             68738                0            39568
>             66051                0            42255
>             63406                0            44900
>             60643                0            47663
>             57954                0            50352
>             55264                0            53042
>             52592                0            55715
>             49922                0            58385
> That is what I get when copying /dev/zero to NFS.
> 
> You can find vmmon.c in Andrew Morton's ext3-tools package.
> Also attached for your convenience.
> 
> I'm very interested in Google's use case for this patch, and why
> the simple /proc/vmstat based vmmon tool is not enough.
> 
> Thanks,
> Fengguang
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