From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joe Thornber <thornber@redhat.com>
Subject: Re: [PATCH] dm-kcopyd/dm-snap: Don't read the origin on
 full chunk write
Date: Mon, 20 Jun 2011 09:09:53 +0100
Message-ID: <20110620080952.GA3266@ubuntu>
References: <Pine.LNX.4.64.1106170829390.24411@hs20-bc2-1.build.redhat.com>
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Cc: "Alasdair G. Kergon" <agk@redhat.com>
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On Fri, Jun 17, 2011 at 08:32:36AM -0400, Mikulas Patocka wrote:
> Hi
> 
> This optimizes full chunk writes for snapshots.
> 
> Note that there is a performance bug in device mapper that it doesn't ever 
> send bios larger than 4k to snapshots. So this patch optimizes only 4k 
> chunk sizes. Once the 4k limit will be removed from device mapper, this 
> patch could optimize any chunk size.

Nack.  If you don't need to copy, don't send it to kcopyd.

- Joe