Re: [PATCH v3 1/3] mm: document zone device struct page field usage

From: Jason Gunthorpe
Date: Wed Jul 24 2019 - 21:23:15 EST

On Wed, Jul 24, 2019 at 04:26:58PM -0700, Ralph Campbell wrote:
> 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.
> Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
> Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
> Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> include/linux/mm_types.h | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)

Ralph, you marked some of thes patches as mm/hmm, but I feel it is
best if Andrew takes them through the normal -mm path.

They don't touch hmm.c or mmu notifiers so I don't forsee conflicts,
and I don't feel comfortable to review this code.