[1/3] mm: document zone device struct page reserved fields
diff mbox series

Message ID 20190719190649.30096-2-rcampbell@nvidia.com
State New
Headers show
  • mm/hmm: fixes for device private page migration
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Commit Message

Ralph Campbell July 19, 2019, 7:06 p.m. UTC
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 <rcampbell@nvidia.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
 include/linux/mm_types.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff mbox series

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. */