linux-kernel - Re: [PATCH 14/14] x86, mm: Put pagetable on local node ram

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Date:	Thu, 7 Mar 2013 23:44:18 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Renninger <trenn@...e.de>,
	Tang Chen <tangchen@...fujitsu.com>,
	linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
	Jacob Shin <jacob.shin@....com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH 14/14] x86, mm: Put pagetable on local node ram

On Thu, Mar 7, 2013 at 11:01 PM, Tejun Heo <tj@...nel.org> wrote:
> On Thu, Mar 07, 2013 at 08:58:40PM -0800, Yinghai Lu wrote:
>> If node with ram is hotplugable, local node mem for page table and vmemmap
>> should be on that node ram.
>>
>> This patch is some kind of refreshment of
>> | commit 1411e0ec3123ae4c4ead6bfc9fe3ee5a3ae5c327
>> | Date:   Mon Dec 27 16:48:17 2010 -0800
>> |
>> |    x86-64, numa: Put pgtable to local node memory
>> That was reverted before.
>>
>> We have reason to reintroduce it to make memory hotplug work.
>>
>> Split calling of init_mem_mapping into early_initmem_info
>> for nodes after we get numa info there.
>>
>> First node will be low range.
>> Need to rework alloc_low_pages to alloc page table in following order:
>>       BRK, local node, low range
>>
>> Still only load_cr3 one time, otherwise we would break xen 64bit again.
>
> Hmmm... can you please split this patch further?  init_mem_mapping()
> change can be separated, no?

will try to split it out.

> Also, comments are disturbingly missing.
> How are other people reading the code supposed to know what it's
> trying to achieve why and how?  Hmmm... we're also likely to end up
> with smaller mapping for misaligned NUMA configurations (I think my
> test machine is like that).  Is it guaranteed that the top level ends
> up in the first node?  It really needs documentation.

Yes. To really memory hotplug working, will need to trim the node
alignment to be
1G in memblock and numa_meminfo.

also need to put pgd page in low range (first node) if 512G block is
crossing node.
for example: if node2 is [256g, 1024g), pgd for 256g-512g, must be stay on node0
and 512g-1024g could stay on node2.
or just put all PGD pages on low range (first node).

Thanks

Yinghai
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