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

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Message-ID: <20110204150456.GD32190@redhat.com>
Date:	Fri, 4 Feb 2011 10:04:57 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jens Axboe <jaxboe@...ionio.com>,
	Mike Snitzer <snitzer@...hat.com>,
	"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>
Subject: Re: [PATCH v3 1/2] block: skip elevator data initialization for
 flush requests

On Thu, Feb 03, 2011 at 02:38:20PM +0100, Tejun Heo wrote:
> Hey, Jens.
> 
> On Thu, Feb 03, 2011 at 02:24:42PM +0100, Jens Axboe wrote:
> > On 2011-02-02 23:55, Mike Snitzer wrote:
> > > 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.
> 
> The rationale behind suggesting was that it indicates to the allocator
> that the request may be sorted as how the request will be used is
> communicated using @rw_flags to the allocator.  The patch is buggy
> that the flag actually ends up on the request.  Any better idea how to
> communicate it?

Though you did not like the V1 of patch, personally I also liked just parsing
FLUSH or FUA flag in get_request().

Or how about intoducing a helper function blk_rq_should_init_elevator() 
or something like that and this function will parse FLUSH, FUA flags.

Thanks
Vivek
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