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Date: Tue, 31 Jan 2012 18:57:54 +0800
From: Wu Fengguang <wfg@linux.intel.com>
To: Christoph Hellwig <hch@infradead.org>
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: <20120131105754.GA3867@localhost>
References: <1327996780.21268.42.camel@sli10-conroe>
 <20120131103416.GA1661@localhost>
 <20120131104621.GA27003@infradead.org>
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On Tue, Jan 31, 2012 at 05:46:21AM -0500, Christoph Hellwig wrote:
> 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.

The problem is, there are a dozen of ->direct_IO callback functions.
While there are only two ->direct_IO() callers, one for READ and
another for WRITE, which are much easier to deal with.

Thanks,
Fengguang