linux-kernel - Re: [PATCH 14/45] writeback: quit on wrap for .range

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Date:	Wed, 7 Oct 2009 12:21:30 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	David Howells <dhowells@...hat.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Li Shaohua <shaohua.li@...el.com>,
	Myklebust Trond <Trond.Myklebust@...app.com>,
	"jens.axboe@...cle.com" <jens.axboe@...cle.com>,
	Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 14/45] writeback: quit on wrap for .range_cyclic (afs)

On Wed, Oct 07, 2009 at 11:17:06AM +0100, David Howells wrote:
> Wu Fengguang <fengguang.wu@...el.com> wrote:
> 
> > Convert wbc.range_cyclic to new behavior: when past EOF, abort writeback
> > of the inode, which instructs writeback_single_inode() to delay it for
> > a while if necessary.
> > 
> > It removes one inefficient .range_cyclic IO pattern when writeback_index
> > wraps:
> > 	submit [10000-10100], (wrap), submit [0-100]
> > In which the submitted pages may be consisted of two distant ranges.
> > 
> > It also prevents submitting pointless IO for busy overwriters.
> > 
> > CC: David Howells <dhowells@...hat.com>
> > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> 
> Acked-by: David Howells <dhowells@...hat.com>

I don't see why. Then the inode is given less write bandwidth than
those which don't wrap (or wrap on "nice" boundaries).

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