linux-kernel - Re: [PATCH] fix readahead pipeline break caused by block plug

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Message-ID: <20120131105754.GA3867@localhost>
Date:	Tue, 31 Jan 2012 18:57:54 +0800
From:	Wu Fengguang <wfg@...ux.intel.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Shaohua Li <shaohua.li@...el.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH] fix readahead pipeline break caused by block plug

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
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