From: Hugh Dickins hughd@google.com Subject: 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/alpine.LSU.2.11.1811261522040.2275@eggly.anvils Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages") Signed-off-by: Hugh Dickins hughd@google.com Reviewed-by: Matthew Wilcox willy@infradead.org Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Jerome Glisse jglisse@redhat.com Cc: Konstantin Khlebnikov khlebnikov@yandex-team.ru Cc: stable@vger.kernel.org [4.8+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/khugepaged.c | 11 +++++++++++ 1 file changed, 11 insertions(+)

--- a/mm/khugepaged.c~mm-khugepaged-collapse_shmem-stop-if-punched-or-truncated +++ a/mm/khugepaged.c @@ -1359,6 +1359,17 @@ static void collapse_shmem(struct mm_str

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; _