linux-kernel - Re: [PATCH] memory hotplug: Speed up add/remove when blocks are larger than PAGES_PER

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Date:	Wed, 11 May 2011 15:21:57 -0700
From:	Greg KH <greg@...ah.com>
To:	Anton Blanchard <anton@...ba.org>
Cc:	gregkh@...e.de, nfont@...tin.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memory hotplug: Speed up add/remove when blocks are
 larger than PAGES_PER_SECTION

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.
> 
> Signed-off-by: Anton Blanchard <anton@...ba.org>

Your patch introduced a compiler warning, care to send a follow-on patch
fixing this up:
	drivers/base/memory.c: In function ‘memory_block_change_state’:
	drivers/base/memory.c:281:6: warning: unused variable ‘i’

thanks,

greg k-h
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