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

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Date:	Thu, 4 Jun 2015 17:09:03 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Xishi Qiu <qiuxishi@...wei.com>,
	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>
CC:	Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH 10/12] mm: add the buddy system interface

+#ifdef CONFIG_MEMORY_MIRROR
+	if (change_to_mirror(gfp_mask, ac.high_zoneidx))
+		ac.migratetype = MIGRATE_MIRROR;
+#endif

We may have to be smarter than this here. I'd like to encourage the
enterprise Linux distributions to set CONFIG_MEMORY_MIRROR=y
But the reality is that most systems will not configure any mirrored
memory - so we don't want the common code path for memory
allocation to call functions that set the migrate type, try to allocate
and then fall back to a non-mirror when that may be a complete waste
of time.

Maybe a global "got_mirror" that is true if we have some mirrored
memory.  Then code is

	if (got_mirror && change_to_mirror(...))
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