From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [RFC][PATCH 5/7] writeback: use 64MB MAX_WRITEBACK_PAGES
Date: Thu, 10 Sep 2009 06:53:18 +0200
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References: <20090909145141.293229693@intel.com>
	 <20090909150600.874037375@intel.com>  <20090909232938.GD24951@mit.edu>
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Cc: Wu Fengguang <fengguang.wu@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jens Axboe <jens.axboe@oracle.com>,
	Dave Chinner <david@fromorbit.com>,
	Chris Mason <chris.mason@oracle.com>,
	Christoph Hellwig <hch@infradead.org>, jack@suse.cz,
	Artem Bityutskiy <dedekind1@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org
To: Theodore Tso <tytso@mit.edu>
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On Wed, 2009-09-09 at 19:29 -0400, Theodore Tso wrote:
> On Wed, Sep 09, 2009 at 10:51:46PM +0800, Wu Fengguang wrote:
> > + * The maximum number of pages to writeout in a single periodic/background
> > + * writeback operation. 64MB means I_SYNC may be hold for up to 1 second.
> > + * This is not a big problem since we normally do kind of trylock on I_SYNC
> > + * for non-data-integrity writes.  Userspace tasks doing throttled writeback
> > + * do not use this value.
> 
> What's your justification for using 64MB?  Where are you getting 1
> second from?  On a fast RAID array 64MB can be written in much less
> than 1 second.

Worse, on my 5mb/s usb stick writing out 64m will take forever.