From mboxrd@z Thu Jan  1 00:00:00 1970
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: Bug 12309 - Large I/O operations result in poor interactive performance and high iowait times
Date: Tue,  3 Aug 2010 15:35:35 +0900 (JST)
Message-ID: <20100803153420.39FD.A69D9226@jp.fujitsu.com>
References: <20100802171954.4F95.A69D9226@jp.fujitsu.com> <20100802115748.GA5308@localhost>
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Cc: 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
To: Wu Fengguang <fengguang.wu@intel.com>
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> > It mean congestion ignorerance is happend when followings
> >   (1) the task is kswapd
> >   (2) the task is flusher thread
> >   (3) this reclaim is called from zone reclaim (note: I'm thinking this is bug)
> >   (4) this reclaim is called from __generic_file_aio_write()
> > 
> > (4) is root cause of this latency issue. this behavior was introduced
> > by following.
> 
> Yes and no.
> 
> (1)-(4) are good summaries for regular files. 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.

Oops. I missed that. thanks correct me!




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