mm/khugepaged: collapse_shmem() remember to clear holes

commit 2af8ff291848cc4b1cce24b6c943394eb2c761e8 upstream.

Huge tmpfs testing reminds us that there is no __GFP_ZERO in the gfp
flags khugepaged uses to allocate a huge page - in all common cases it
would just be a waste of effort - so collapse_shmem() must remember to
clear out any holes that it instantiates.

The obvious place to do so, where they are put into the page cache tree,
is not a good choice: because interrupts are disabled there.  Leave it
until further down, once success is assured, where the other pages are
copied (before setting PageUptodate).

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261525080.2275@eggly.anvils
Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org>	[4.8+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 3f7bfd98b0e6b64a6e8ce97f10dcc4e561e13eba..2d3ce49f6b450368c5b5e8e5d5b293e7ffcc49d2 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1501,7 +1501,12 @@ tree_unlocked:
                 * Replacing old pages with new one has succeed, now we need to
                 * copy the content and free old pages.
                 */
+               index = start;
                list_for_each_entry_safe(page, tmp, &pagelist, lru) {
+                       while (index < page->index) {
+                               clear_highpage(new_page + (index % HPAGE_PMD_NR));
+                               index++;
+                       }
                        copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
                                        page);
                        list_del(&page->lru);
@@ -1511,6 +1516,11 @@ tree_unlocked:
                        ClearPageActive(page);
                        ClearPageUnevictable(page);
                        put_page(page);
+                       index++;
+               }
+               while (index < end) {
+                       clear_highpage(new_page + (index % HPAGE_PMD_NR));
+                       index++;
                }
 
                local_irq_save(flags);