Messages in this thread Patch in this message | | | From | Ralph Campbell <> | Subject | [PATCH 1/3] mm: document zone device struct page reserved fields | Date | Fri, 19 Jul 2019 12:06:47 -0700 |
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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 --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
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