mm: migrate: fix THP's mapcount on isolation

The issue is reported when removing memory through virtio_mem device.  The
transparent huge page, experienced copy-on-write fault, is wrongly
regarded as pinned.  The transparent huge page is escaped from being
isolated in isolate_migratepages_block().  The transparent huge page can't
be migrated and the corresponding memory block can't be put into offline
state.

Fix it by replacing page_mapcount() with total_mapcount().  With this, the
transparent huge page can be isolated and migrated, and the memory block
can be put into offline state.  Besides, The page's refcount is increased
a bit earlier to avoid the page is released when the check is executed.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 1da2f328fa64 ("mm,thp,compaction,cma: allow THP migration for CMA allocations")
Signed-off-by: Gavin Shan <[email protected]>
Reported-by: Zhenyu Zhang <[email protected]>
Tested-by: Zhenyu Zhang <[email protected]>
Suggested-by: David Hildenbrand <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: William Kucharski <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: <[email protected]>	[5.7+]
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions