linux-ext4 - Re: [PATCH v3 1/2] block: skip elevator data initialization for flush requests

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Date:	Thu, 3 Feb 2011 10:28:23 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	Jens Axboe <jaxboe@...ionio.com>, tytso@....edu, djwong@...ibm.com,
	shli@...nel.org, neilb@...e.de, adilger.kernel@...ger.ca,
	jack@...e.cz, linux-kernel@...r.kernel.org, kmannth@...ibm.com,
	cmm@...ibm.com, linux-ext4@...r.kernel.org, rwheeler@...hat.com,
	hch@....de, josef@...hat.com, jmoyer@...hat.com, vgoyal@...hat.com
Subject: Re: [PATCH v3 1/2] block: skip elevator data initialization for
 flush requests

Hello,

On Wed, Feb 02, 2011 at 05:55:49PM -0500, Mike Snitzer wrote:
> @@ -808,9 +808,14 @@ static struct request *get_request(struc
>  	rl->count[is_sync]++;
>  	rl->starved[is_sync] = 0;
>  
> -	priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
> -	if (priv)
> -		rl->elvpriv++;
> +	/*
> +	 * Only initialize elevator data if REQ_SORTED is set.
> +	 */
> +	if (rw_flags & REQ_SORTED) {
> +		priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
> +		if (priv)
> +			rl->elvpriv++;
> +	}

This isn't enough.  Now the allocated requests would have REQ_SORTED
set before going into elevator.  You probably want to filter out
REQ_SORTED to elv_may_queue() too.

Also, it would be great if you update the comment on top of
get_request() to explain what @rw_flags does.

Thank you.

-- 
tejun
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