linux-kernel - Re: [RFC][PATCH 5/7] writeback: use 64MB MAX_WRITEBACK

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Message-ID: <20090909232938.GD24951@mit.edu>
Date:	Wed, 9 Sep 2009 19:29:38 -0400
From:	Theodore Tso <tytso@....edu>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>, jack@...e.cz,
	Artem Bityutskiy <dedekind1@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [RFC][PATCH 5/7] writeback: use 64MB MAX_WRITEBACK_PAGES

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.

More generally, I assume your patches conflict with Jens' per-bdi patches?

     		  	      	      	       - Ted
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