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From: Miklos Szeredi <miklos@szeredi.hu>
To: akpm@linux-foundation.org
Cc: miklos@szeredi.hu, a.p.zijlstra@chello.nl,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [patch 6/6] mm: bdi: allow setting a maximum for the bdi dirty limit
Date: Thu, 31 Jan 2008 10:46:50 +0100	[thread overview]
Message-ID: <E1JKW0Q-000200-An@pomaz-ex.szeredi.hu> (raw)
In-Reply-To: <20080130163927.760e94cc.akpm@linux-foundation.org> (message from Andrew Morton on Wed, 30 Jan 2008 16:39:27 -0800)

> On Tue, 29 Jan 2008 16:49:06 +0100
> Miklos Szeredi <miklos@szeredi.hu> wrote:
> 
> > Add "max_ratio" to /sys/class/bdi.  This indicates the maximum
> > percentage of the global dirty threshold allocated to this bdi.
> 
> Maybe I'm having a stupid day, but I don't understand the semantics of this
> min and max at all.  I've read the code, and I've read the comments (well,
> I've hunted for some) and I've read the docs.
> 
> I really don't know how anyone could use this in its current state without
> doing a lot of code-reading and complex experimentation.  All of which
> would be unneeded if this tunable was properly documented.
> 
> So.  Please provide adequate documentation for this tunable.  I'd suggest
> that it be pitched at the level of a reasonably competent system operator. 
> It should help them understand why the tunable exists, why they might
> choose to alter it, and what effects they can expect to see.  Hopefully a
> reaonably competent kernel developer can then understand it too.

OK.  I think what's missing from some docs, is a high level
description of the per-bdi throttling algorithm, and how it affects
writeback.  Because with info, I think the min and max ratios are
trivially understandable: they just override the result of the
algorithm, in case it would mean too high or too low threshold.

Peter, could you write something about that?

Thanks,
Miklos

  reply	other threads:[~2008-01-31  9:47 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-29 15:49 [patch 0/6] mm: bdi: updates Miklos Szeredi
2008-01-29 15:49 ` [patch 1/6] mm: bdi: tweak task dirty penalty Miklos Szeredi
2008-01-31  0:13   ` Andrew Morton
2008-01-29 15:49 ` [patch 2/6] mm: bdi: export BDI attributes in sysfs Miklos Szeredi
2008-01-29 17:39   ` Greg KH
2008-01-31  0:28   ` Andrew Morton
2008-01-31  9:39     ` Miklos Szeredi
2008-01-31  9:54       ` Andrew Morton
2008-01-31 10:08         ` Peter Zijlstra
2008-02-29 11:26   ` Andrew Morton
2008-01-29 15:49 ` [patch 3/6] mm: bdi: expose the BDI object in sysfs for NFS Miklos Szeredi
2008-01-29 15:49 ` [patch 4/6] mm: bdi: expose the BDI object in sysfs for FUSE Miklos Szeredi
2008-01-29 15:49 ` [patch 5/6] mm: bdi: allow setting a minimum for the bdi dirty limit Miklos Szeredi
2008-01-29 15:49 ` [patch 6/6] mm: bdi: allow setting a maximum " Miklos Szeredi
2008-01-31  0:39   ` Andrew Morton
2008-01-31  9:46     ` Miklos Szeredi [this message]
2008-01-31 10:17       ` Peter Zijlstra
2008-01-29 17:06 ` [patch 0/6] mm: bdi: updates Peter Zijlstra
2008-01-29 18:32   ` Miklos Szeredi

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