linux-kernel - Re: [Patch 001/002] Make description of memory hotplug notifier in document

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Message-ID: <Pine.LNX.4.64.0710112110590.1882@schroedinger.engr.sgi.com>
Date:	Thu, 11 Oct 2007 21:18:40 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Yasunori Goto <y-goto@...fujitsu.com>
cc:	Andrew Morton <akpm@...l.org>,
	Hiroyuki KAMEZAWA <kamezawa.hiroyu@...fujitsu.com>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [Patch 001/002] Make description of memory hotplug notifier in
 document

Looks good. Some suggestions on improving the wording.

On Fri, 12 Oct 2007, Yasunori Goto wrote:

> +MEMORY_GOING_ONLINE
> +  This is notified before memory online. If some structures must be prepared
> +  for new memory, it should be done at this event's callback.
> +  The new onlining memory can't be used yet.

Generated before new memory becomes available in order to be able to 
prepare subsystems to handle memory. The page allocator is still unable
to allocate from the new memory.

> +MEMORY_CANCEL_ONLINE
> +  If memory online fails, this event is notified for rollback of setting at
> +  MEMORY_GOING_ONLINE.
> +  (Currently, this event is notified only the case which a callback routine
> +   of MEMORY_GOING_ONLINE fails).

Generated if MEMORY_GOING_ONLINE fails.

> +MEMORY_ONLINE
> +  This event is called when memory online is completed. The page allocator uses
> +  new memory area before this notification. In other words, callback routine
> +  use new memory area via page allocator.
> +  The failures of callbacks of this notification will be ignored.

Generated when memory has succesfully brought online. The callback may 
allocate from the new memory.

> +MEMORY_GOING_OFFLINE
> +  This is notified on halfway of memory offline. The offlining pages are
> +  isolated. In other words, the page allocater doesn't allocate new pages from
> +  offlining memory area at this time. If callback routine freed some pages,
> +  they are not used by the page allocator.
> +  This is good place for shrinking cache. (If possible, it is desirable to
> +  migrate to other area.)

Generated to begin the process of offlining memory. Allocations are no 
longer possible from the memory but some of the memory to be offlined
is still in use. The callback can be used to free memory known to a 
subsystem from the indicated node.

> +MEMORY_CANCEL_OFFLINE
> +  If memory offline fails, this event is notified for rollback against
> +  MEMORY_GOING_OFFLINE. The page allocator will use target memory area after
> +  this callback again.

Generated if MEMORY_GOING_OFFLINE fails. Memory is available again from 
the node that we attempted to offline.

> + +MEMORY_OFFLINE

Generated after offlining memory is complete.
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