From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: Bug 12309 - Large I/O operations result in poor interactive
 performance and high iowait times
Date: Tue, 3 Aug 2010 08:45:11 +0800
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Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	Andrew Clayton <andrew@digital-domain.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mel@csn.ul.ie>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Dave Chinner <david@fromorbit.com>,
	Chris Mason <chris.mason@oracle.com>, Nick Piggin <npiggin@suse.de>,
	Rik van Riel <riel@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>, Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@infradead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	"pvz@pvz.pp.se" <pvz@pvz.pp.se>,
	"bgamari@gmail.com" <bgamari@gmail.com>,
	"larppaxyz@gmail.com" <larppaxyz@gmail.com>,
	"seanj@xyke.com" <seanj@xyke.com>,
	"kernel-bugs.dev1world@spamgourmet.com" <kernel-bugs
To: Minchan Kim <minchan.kim@gmail.com>
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> > What in my mind is (without any throttling)
> >
> > =C2=A0 =C2=A0 =C2=A0 =C2=A0if (PageSwapcache(page)) {
> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0if (bdi_write_=
congested(bdi))
>=20
> You mentioned following as.
>=20
> "However !bdi_write_congested(bdi) is now unconditionally true for the
> swapper_space, which means any process can do swap out to a congested
> queue and block there."
>=20
> But you used bdi_write_congested in here.
> Which is right?

Ah sorry, I was also cheated by the name.. bdi_write_congested()
won't work for swap_backing_dev_info.  Anyway you may take it as
"pseudo" code :)

Thanks,
Fengguang

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