mm/khugepaged: collapse_shmem() stop if punched or truncated

Huge tmpfs testing showed that although collapse_shmem() recognizes a concurrently truncated or hole-punched page correctly, its handling of holes was liable to refill an emptied extent. Add check to stop that. Link: http://lkml.kernel.org/r/[email protected] Fixes: f3f0e1d ("khugepaged: add support of collapse for tmpfs/shmem pages") Signed-off-by: Hugh Dickins <[email protected]> Reviewed-by: Matthew Wilcox <[email protected]> Cc: Kirill A. Shutemov <[email protected]> Cc: Jerome Glisse <[email protected]> Cc: Konstantin Khlebnikov <[email protected]> Cc: <[email protected]> [4.8+] Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
allenpais · Nov 30, 2018 · 701270f · 701270f
1 parent 006d3ff
commit 701270f
Showing 1 changed file with 11 additions and 0 deletions.
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
@@ -1359,6 +1359,17 @@ static void collapse_shmem(struct mm_struct *mm,
 
 		VM_BUG_ON(index != xas.xa_index);
 		if (!page) {
+			/*
+			 * Stop if extent has been truncated or hole-punched,
+			 * and is now completely empty.
+			 */
+			if (index == start) {
+				if (!xas_next_entry(&xas, end - 1)) {
+					result = SCAN_TRUNCATED;
+					break;
+				}
+				xas_set(&xas, index);
+			}
 			if (!shmem_charge(mapping->host, 1)) {
 				result = SCAN_FAIL;
 				break;