Date: Wed, 11 May 2011 08:19:00 -0700
From: Greg KH <gregkh@suse.de>
To: Anton Blanchard <anton@samba.org>
Cc: nfont@austin.ibm.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memory hotplug: Speed up add/remove when blocks are
 larger than PAGES_PER_SECTION
Message-ID: <20110511151900.GA19603@suse.de>
References: <20110511172514.7e30970d@kryten>
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On Wed, May 11, 2011 at 05:25:14PM +1000, Anton Blanchard wrote:
> 
> On ppc64 the minimum memory section for hotplug is 16MB but most
> recent machines have a memory block size of 256MB. This means
> memory_block_change_state does 16 separate calls to
> memory_section_action.
> 
> This also means we call the notifiers 16 times and the hook
> in the ehea network driver is quite costly. To offline one 256MB
> region takes:
> 
> # time echo offline > /sys/devices/system/memory/memory32/state
> 7.9s
> 
> This patch removes the loop and calls online_pages or
> remove_memory once for the entire region and in doing so makes
> the logic simpler since we don't have to back out if things fail
> part way through.
> 
> The same test to offline one region now takes:
> 
> # time echo online > /sys/devices/system/memory/memory32/state
> 0.67s
> 
> Over 11 times faster.

Very nice job, I'll queue this up for .40.

thanks,

greg k-h
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