Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/3] mm: document zone device struct page reserved fields | From | John Hubbard <> | Date | Tue, 16 Jul 2019 18:20:23 -0700 |
| |
On 7/16/19 5:14 PM, Ralph Campbell wrote: > 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 */
Actually, I do think this helps. It's hard to document these fields, and the ZONE_DEVICE pages have a really complicated situation during migration to a device.
Additionally, I'm not sure, but should we go even further, and do this on the other side of the alias:
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index d6ea74e20306..c5ce5989d8a8 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -83,7 +83,12 @@ struct page { * by the page owner. */ struct list_head lru; - /* See page-flags.h for PAGE_MAPPING_FLAGS */ + /* + * See page-flags.h for PAGE_MAPPING_FLAGS. + * + * Also: the next three fields (mapping, index and + * private) are all used by ZONE_DEVICE pages. + */ struct address_space *mapping; pgoff_t index; /* Our offset within mapping. */ /** ?
Either way, you can add:
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
thanks, -- John Hubbard NVIDIA
| |