mm/migrate.c: remove MIGRATE_PFN_LOCKED

MIGRATE_PFN_LOCKED is used to indicate to migrate_vma_prepare() that a
source page was already locked during migrate_vma_collect().  If it
wasn't then the a second attempt is made to lock the page.  However if
the first attempt failed it's unlikely a second attempt will succeed,
and the retry adds complexity.  So clean this up by removing the retry
and MIGRATE_PFN_LOCKED flag.

Destination pages are also meant to have the MIGRATE_PFN_LOCKED flag
set, but nothing actually checks that.

Link: https://lkml.kernel.org/r/20211025041608.289017-1-apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index a14c2938e7af..f2a59ed82ed3 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -360,7 +360,7 @@ between device driver specific code and shared common code:
    system memory page, locks the page with ``lock_page()``, and fills in the
    ``dst`` array entry with::
 
-     dst[i] = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED;
+     dst[i] = migrate_pfn(page_to_pfn(dpage));
 
    Now that the driver knows that this page is being migrated, it can
    invalidate device private MMU mappings and copy device private memory