From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Snitzer <snitzer@redhat.com>
Subject: Re: [PATCH v2 7/7] dm snapshot: use bufio prefetch
Date: Mon, 13 Jan 2014 18:59:28 -0500
Message-ID: <20140113235928.GA4789@redhat.com>
References: <alpine.LRH.2.02.1401111229150.4018@file01.intranet.prod.int.rdu2.redhat.com>
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	<alpine.LRH.2.02.1401111230080.4018@file01.intranet.prod.int.rdu2.redhat.com>
	<alpine.LRH.2.02.1401111230330.4018@file01.intranet.prod.int.rdu2.redhat.com>
	<alpine.LRH.2.02.1401111231000.4018@file01.intranet.prod.int.rdu2.redhat.com>
	<alpine.LRH.2.02.1401111231420.4018@file01.intranet.prod.int.rdu2.redhat.com>
	<20140113213758.GC3268@redhat.com>
	<alpine.LRH.2.02.1401131659250.12957@file01.intranet.prod.int.rdu2.redhat.com>
	<20140113225651.GA1678@redhat.com>
	<alpine.LRH.2.02.1401131843470.26646@file01.intranet.prod.int.rdu2.redhat.com>
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To: Mikulas Patocka <mpatocka@redhat.com>
Cc: dm-devel@redhat.com, "Alasdair G. Kergon" <agk@redhat.com>
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On Mon, Jan 13 2014 at  6:45pm -0500,
Mikulas Patocka <mpatocka@redhat.com> wrote:

> 
> 
> On Mon, 13 Jan 2014, Mike Snitzer wrote:
> 
> > On Mon, Jan 13 2014 at  5:00pm -0500,
> > Mikulas Patocka <mpatocka@redhat.com> wrote:
> > 
> > > No.
> > > 
> > > This changed patch inefficiently loops in bufio_prefetch_chunks for each 
> > > buffer that is read.
> > 
> > Yeah, I overlooked the importance of preserving prefetch_area (which
> > explains the unlikely you had).  But my intent was to make your code
> > less "special"; your if (DM_PREFETCH_CHUNKS) do { } while() code to
> > avoid the extra indentation is pretty ugly.
> > 
> > Given your current code, DM_PREFETCH_CHUNKS is always 12 so why not just
> > remove the check?
> 
> If someone ever changes it to a variable, the condition is there avoid 
> unneeded call to dm_bufio_prefetch. The compiler optimizes out the 
> constant expression, so it doesn't matter that it's there.

How about move the conditional inside the do { } ?

I really dislike the style you've used on this, is there anywhere else
in the kernel that does this?