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authorRalph Campbell <rcampbell@nvidia.com>2019-08-14 01:37:04 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2019-08-14 02:06:52 +0300
commit76470ccd62f18bfa0954bec10f2329339f793914 (patch)
tree72d5ecefb991a588c39bf47eca9ad178337ff459 /include
parentd45331b00ddb179e291766617259261c112db872 (diff)
downloadlinux-76470ccd62f18bfa0954bec10f2329339f793914.tar.xz
mm: document zone device struct page field usage
Patch series "mm/hmm: fixes for device private page migration", v3. Testing the latest linux git tree turned up a few bugs with page migration to and from ZONE_DEVICE private and anonymous pages. Hopefully it clarifies how ZONE_DEVICE private struct page uses the same mapping and index fields from the source anonymous page mapping. This patch (of 3): Struct page for ZONE_DEVICE private pages uses the page->mapping and and page->index fields while the source anonymous pages are migrated to device private memory. This is so rmap_walk() can find the page when migrating the ZONE_DEVICE private page back to system memory. ZONE_DEVICE pmem backed fsdax pages also use the page->mapping and page->index fields when files are mapped into a process address space. Add comments to struct page and remove the unused "_zd_pad_1" field to make this more clear. Link: http://lkml.kernel.org/r/20190724232700.23327-2-rcampbell@nvidia.com Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> 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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/mm_types.h11
1 files changed, 10 insertions, 1 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 3a37a89eb7a7..6a7a1083b6fb 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -159,7 +159,16 @@ 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 */
+ /*
+ * ZONE_DEVICE private pages are counted as being
+ * mapped so the next 3 words hold the mapping, index,
+ * and private fields from the source anonymous or
+ * page cache page while the page is migrated to device
+ * private memory.
+ * ZONE_DEVICE MEMORY_DEVICE_FS_DAX pages also
+ * use the mapping, index, and private fields when
+ * pmem backed DAX files are mapped.
+ */
};
/** @rcu_head: You can use this to free a page by RCU. */