mm/memory-failure: unnecessary amount of unmapping

It appears that unmap_mapping_range() actually takes a 'size' as its third
argument rather than a location, the current calling fashion causes
unnecessary amount of unmapping to occur.

Link: https://lkml.kernel.org/r/20210420002821.2749748-1-jane.chu@oracle.com
Fixes: 6100e34b ("mm, memory_failure: Teach memory_failure() about dev_pagemap pages")
Signed-off-by: NJane Chu <jane.chu@oracle.com>
Reviewed-by: NDan Williams <dan.j.williams@intel.com>
Reviewed-by: NNaoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/memory-failure.c

@@ -1368,7 +1368,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
 		 * communicated in siginfo, see kill_proc()
 		 */
 		start = (page->index << PAGE_SHIFT) & ~(size - 1);
-		unmap_mapping_range(page->mapping, start, start + size, 0);
+		unmap_mapping_range(page->mapping, start, size, 0);
 	}
 	kill_procs(&tokill, flags & MF_MUST_KILL, !unmap_success, pfn, flags);
 	rc = 0;