Struct page for ZONE_DEVICE private pages uses the reserved fields when
anonymous pages are migrated to device private memory. This is so
the page->mapping and page->index fields are preserved and the page can
be migrated back to system memory.
Document this in comments so it is more clear.
Signed-off-by: Ralph Campbell <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Jérôme Glisse <[email protected]>
Cc: "Kirill A . Shutemov" <[email protected]>
Cc: Lai Jiangshan <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
---
include/linux/mm_types.h | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 3a37a89eb7a7..d6ea74e20306 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -159,7 +159,14 @@ struct page {
/** @pgmap: Points to the hosting device page map. */
struct dev_pagemap *pgmap;
void *zone_device_data;
- unsigned long _zd_pad_1; /* uses mapping */
+ /*
+ * The following fields are used to hold the source
+ * page anonymous mapping information while it is
+ * migrated to device memory. See migrate_page().
+ */
+ unsigned long _zd_pad_1; /* aliases mapping */
+ unsigned long _zd_pad_2; /* aliases index */
+ unsigned long _zd_pad_3; /* aliases private */
};
/** @rcu_head: You can use this to free a page by RCU. */
--
2.20.1