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

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Message-ID: <4D4AAC9A.4050407@fusionio.com>
Date:	Thu, 3 Feb 2011 14:24:42 +0100
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Mike Snitzer <snitzer@...hat.com>
CC:	Tejun Heo <tj@...nel.org>, "tytso@....edu" <tytso@....edu>,
	"djwong@...ibm.com" <djwong@...ibm.com>,
	"shli@...nel.org" <shli@...nel.org>,
	"neilb@...e.de" <neilb@...e.de>,
	"adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
	"jack@...e.cz" <jack@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kmannth@...ibm.com" <kmannth@...ibm.com>,
	"cmm@...ibm.com" <cmm@...ibm.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"rwheeler@...hat.com" <rwheeler@...hat.com>,
	"hch@....de" <hch@....de>, "josef@...hat.com" <josef@...hat.com>,
	"jmoyer@...hat.com" <jmoyer@...hat.com>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>
Subject: Re: [PATCH v3 1/2] block: skip elevator data initialization for flush
  requests

On 2011-02-02 23:55, Mike Snitzer wrote:
> Set REQ_SORTED, in the @rw_flags passed to the request allocator, for
> any request that may be put on IO scheduler.  Skip elevator data
> initialization during request allocation if REQ_SORTED is not set.
> 
> REQ_SORTED is not set for flush requests because they are never put on
> the IO scheduler.

That looks very wrong. REQ_SORTED gets set _when_ the request is sorted
into the IO scheduler. This is gross misuse, a bad hack.

-- 
Jens Axboe

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