mm/gup.c: refactor check_and_migrate_movable_pages()

When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() is
called to migrate pages out of zones which should not contain any longterm
pinned pages.

When migration succeeds all pages will have been unpinned so pinning needs
to be retried.  Migration can also fail, in which case the pages will also
have been unpinned but the operation should not be retried.  If all pages
are in the correct zone nothing will be unpinned and no retry is required.

The logic in check_and_migrate_movable_pages() tracks unnecessary state
and the return codes for each case are difficult to follow.  Refactor the
code to clean this up.  No behaviour change is intended.

[[email protected]: fix unused var warning]
Link: https://lkml.kernel.org/r/19583d1df07fdcb99cfa05c265588a3fa58d1902.1661317396.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple <[email protected]>
Reviewed-by: John Hubbard <[email protected]>
Cc: Alex Sierra <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Felix Kuehling <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Logan Gunthorpe <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Ralph Campbell <[email protected]>
Cc: Shigeru Yoshida <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions