linux-kernel - Re: [RFC PATCH] mm: introduce N_LRU_MEMORY to distinguish between normal and movable memory

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Date:	Fri, 10 Aug 2012 09:12:25 -0500 (CDT)
From:	"Christoph Lameter (Open Source)" <cl@...ux.com>
To:	Hanjun Guo <guohanjun@...wei.com>
cc:	Wu Jianguo <wujianguo@...wei.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	Tony Luck <tony.luck@...el.com>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>, Mel Gorman <mgorman@...e.de>,
	Yinghai Lu <yinghai@...nel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	Keping Chen <chenkeping@...wei.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Jiang Liu <liuj97@...il.com>
Subject: Re: [RFC PATCH] mm: introduce N_LRU_MEMORY to distinguish between
 normal and movable memory

On Fri, 10 Aug 2012, Hanjun Guo wrote:

> On 2012/8/9 22:06, Christoph Lameter (Open Source) wrote:
> > On Thu, 9 Aug 2012, Hanjun Guo wrote:
> >
> >> Now, We have node masks for both N_NORMAL_MEMORY and
> >> N_HIGH_MEMORY to distinguish between normal and highmem on platforms such as x86.
> >> But we still don't have such a mechanism to distinguish between "normal" and "movable"
> >> memory.
> >
> > What is the exact difference that you want to establish?
>
> Hi Christoph,
>     Thanks for your comments very much!
>
> We want to identify the node only has ZONE_MOVABLE memory.
> for example:
> 	node 0: ZONE_DMA, ZONE_DMA32, ZONE_NORMAL--> N_LRU_MEMORY, N_NORMAL_MEMORY
> 	node 1: ZONE_MOVABLE			 --> N_LRU_MEMORY
> thus, in SLUB allocator, will not allocate memory control structures for node1.

So this would change the N_NORMAL_MEMORY definition so that N_NORMAL
means !LRU allocs possible? So far N_NORMAL_MEMORY has a wider scope of
meaning. We need an accurate definition of the meaning of all these
attributes.

> > For the slab case that you want to solve here you will need to know if the
> > node has *only* movable memory and will never have any ZONE_NORMAL memory.
> > If so then memory control structures for allocators that do not allow
> > movable memory will not need to be allocated for these node. The node can
> > be excluded from handling.
>
> I think this is what we are trying to do in this patch.
> did I miss something?

THe meaning of ZONE_NORMAL seems to change which causes confusion. Please
describe in detail what each of these attributes mean.
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