linux-kernel - Re: [7/8,v3] NUMA Hotplug Emulator: extend memory probe interface to support NUMA

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Date:	Thu, 18 Nov 2010 08:59:11 -0800
From:	Aaron Durbin <adurbin@...gle.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>, shaohui.zheng@...el.com,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, haicheng.li@...ux.intel.com,
	lethal@...ux-sh.org, ak@...ux.intel.com,
	shaohui.zheng@...ux.intel.com, Haicheng Li <haicheng.li@...el.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Greg KH <greg@...ah.com>
Subject: Re: [7/8,v3] NUMA Hotplug Emulator: extend memory probe interface to
 support NUMA

On Wed, Nov 17, 2010 at 2:44 PM, David Rientjes <rientjes@...gle.com> wrote:
> On Wed, 17 Nov 2010, Dave Hansen wrote:
>
>> > Then, export the amount of memory that is actually physically present in
>> > the e820 but was truncated by mem=
>>
>> I _think_ that's already effectively done in /sys/firmware/memmap.
>>
>
> Ok.
>
> It's a little complicated because we don't export each online node's
> physical address range so you have to parse the dmesg to find what nodes
> were allocated at boot and determine how much physically present memory
> you have that's hidden but can be hotplugged using the probe files.
>
> Adding Aaron Durbin <adurbin@...gle.com> to the cc because he has a patch
> that exports the physical address range of each node in their sysfs
> directories.

Is this something that is needed upstream? I can post it if that is the case.
Sorry, I don't have a lot of context w.r.t. this thread.

>
>> > and allow users to hot-add the memory
>> > via the probe interface.  Add a writeable 'node' file to offlined memory
>> > section directories and allow it to be changed prior to online.
>>
>> That would work, in theory.  But, in practice, we allocate the mem_map[]
>> at probe time.  So, we've already effectively picked a node at probe.
>> That was done because the probe is equivalent to the hardware "add"
>> event.  Once the hardware where in the address space the memory is, it
>> always also knows the node.
>>
>> But, I guess it also wouldn't be horrible if we just hot-removed and
>> hot-added an offline section if someone did write to a node file like
>> you're suggesting.  It might actually exercise some interesting code
>> paths.
>>
>
> Since the pages are offline you should be able to modify the memmap when
> the 'node' file is written and use populate_memnodemap() since that file
> is only writeable in an offline state.
>
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