linux-kernel - [RFC PATCH 1/3] mm,memory_hotplug: Introduce MHP_MEMMAP_ON

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Date:   Thu, 22 Oct 2020 14:58:33 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     david@...hat.com
Cc:     mhocko@...nel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, vbabka@...e.cz, pasha.tatashin@...een.com,
        Oscar Salvador <osalvador@...e.de>
Subject: [RFC PATCH 1/3] mm,memory_hotplug: Introduce MHP_MEMMAP_ON_MEMORY

MHP_MEMMAP_ON_MEMORY tells the system that we want the memmap
pagetables to be built from the hot-added range.

Signed-off-by: Oscar Salvador <osalvador@...e.de>
---
 include/linux/memory_hotplug.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index d65c6fdc5cfc..dda2d0e5d1ba 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -70,6 +70,14 @@ typedef int __bitwise mhp_t;
  */
 #define MEMHP_MERGE_RESOURCE	((__force mhp_t)BIT(0))
 
+/*
+ * We want memmap (struct page array) to be self contained.
+ * To do so, we will use the beginning of the hot-added range to build
+ * the page tables for the memmap array that describes the entire range.
+ * Only selected architectures support it with SPARSE_VMEMMAP.
+ */
+#define MEMHP_MEMMAP_ON_MEMORY	((__force mhp_t)BIT(1))
+
 /*
  * Extended parameters for memory hotplug:
  * altmap: alternative allocator for memmap array (optional)
-- 
2.26.2