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Date: Tue, 31 Jan 2012 05:46:21 -0500
From: Christoph Hellwig <hch@infradead.org>
To: Wu Fengguang <wfg@linux.intel.com>
Cc: Shaohua Li <shaohua.li@intel.com>, lkml <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jens Axboe <axboe@kernel.dk>, Herbert Poetzl <herbert@13thfloor.at>,
        Eric Dumazet <eric.dumazet@gmail.com>, Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH] fix readahead pipeline break caused by block plug
Message-ID: <20120131104621.GA27003@infradead.org>
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On Tue, Jan 31, 2012 at 06:34:16PM +0800, Wu Fengguang wrote:
>  	}
>  
> +	blk_start_plug(&plug);
>  	written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
> +	blk_finish_plug(&plug);

Please move the plugging into ->direct_IO for both read and write, as
that is the boundary between generic highlevel code, and low-level block
code that should know about plugs.