Commit 701270fa authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds

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.

Fixes: f3f0e1d2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: default avatarHugh Dickins <>
Reviewed-by: default avatarMatthew Wilcox <>
Cc: Kirill A. Shutemov <>
Cc: Jerome Glisse <>
Cc: Konstantin Khlebnikov <>
Cc: <>	[4.8+]
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 006d3ff2
......@@ -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)) {
xas_set(&xas, index);
if (!shmem_charge(mapping->host, 1)) {
result = SCAN_FAIL;
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