[PATCH 4.14 007/146] mm/khugepaged: collapse_shmem() remember to clear holes

From: Greg Kroah-Hartman
Date: Tue Dec 04 2018 - 06:02:12 EST


4.14-stable review patch. If anyone has any objections, please let me know.

------------------

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@xxxxxxxxxxxx
Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.8+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
mm/khugepaged.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index be7b0863e33c..f535dbe3f9f5 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1502,7 +1502,12 @@ static void collapse_shmem(struct mm_struct *mm,
* 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);
@@ -1512,6 +1517,11 @@ static void collapse_shmem(struct mm_struct *mm,
ClearPageActive(page);
ClearPageUnevictable(page);
put_page(page);
+ index++;
+ }
+ while (index < end) {
+ clear_highpage(new_page + (index % HPAGE_PMD_NR));
+ index++;
}

local_irq_save(flags);
--
2.17.1