linux-kernel - [PATCH] mm: ZONE_DEVICE depends on SPARSEMEM

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Message-ID: <20160305004214.12356.32017.stgit@dwillia2-desk3.jf.intel.com>
Date:	Fri, 04 Mar 2016 16:42:14 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	akpm@...ux-foundation.org
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH] mm: ZONE_DEVICE depends on SPARSEMEM_VMEMMAP

The primary use case for devm_memremap_pages() is to allocate an
memmap array from persistent memory.  That capabilty requires
vmem_altmap which requires SPARSEMEM_VMEMMAP.

Also, without SPARSEMEM_VMEMMAP the addition of ZONE_DEVICE expands
ZONES_WIDTH and triggers the:

"Unfortunate NUMA and NUMA Balancing config, growing page-frame for
last_cpupid."

...warning in mm/memory.c.  SPARSEMEM_VMEMMAP=n && ZONE_DEVICE=y is not
a configuration we should worry about supporting.

Reported-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 mm/Kconfig |    1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index 664fa2416909..b95322ba542b 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -654,6 +654,7 @@ config ZONE_DEVICE
 	bool "Device memory (pmem, etc...) hotplug support" if EXPERT
 	depends on MEMORY_HOTPLUG
 	depends on MEMORY_HOTREMOVE
+	depends on SPARSEMEM_VMEMMAP
 	depends on X86_64 #arch_add_memory() comprehends device memory
 
 	help