linux-kernel - RE: [RFC PATCH 10/12] mm: add the buddy system interface

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Date:	Wed, 10 Jun 2015 20:40:08 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Xishi Qiu <qiuxishi@...wei.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"nao.horiguchi@...il.com" <nao.horiguchi@...il.com>,
	Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"mingo@...e.hu" <mingo@...e.hu>, Xiexiuqi <xiexiuqi@...wei.com>,
	Hanjun Guo <guohanjun@...wei.com>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH 10/12] mm: add the buddy system interface

> I guess, mirrored memory should be allocated if !__GFP_HIGHMEM or !__GFP_MOVABLE

HIGHMEM shouldn't matter - partial memory mirror only makes any sense on X86_64 systems ... 32-bit kernels
don't even boot on systems with 64GB, and the minimum rational configuration for a machine that supports
mirror is 128GB (4 cpu sockets * 2 memory controller per socket * 4 channels per controller * 4GB DIMM ...
leaving any channels empty likely leaves you short of memory bandwidth for these high core count processors).

MOVABLE is mostly the opposite of MIRROR - we never want to fill a kernel allocation from a MOVABLE page. I
want all kernel allocations to be from MIRROR.

-Tony

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