Re: [PATCH v2] mm,thp: recheck each page before collapsing file THP

[Johannes Weiner]

On Fri, Oct 18, 2019 at 12:49:46PM -0400, Johannes Weiner wrote:
> On Fri, Oct 18, 2019 at 09:37:54AM -0700, Song Liu wrote:
> > In collapse_file(), after locking the page, it is necessary to recheck
> > that the page is up-to-date. Add PageUptodate() check for both shmem THP
> > and file THP.
> > 
> > Current khugepaged should not try to collapse dirty file THP, because it
> > is limited to read only text. Add a PageDirty check and warning for file
> > THP. This is added after page_mapping() check, because if the page is
> > truncated, it might be dirty.
> > 
> > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> > Cc: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
> > Cc: Johannes Weiner <han...@cmpxchg.org>
> > Cc: Hugh Dickins <hu...@google.com>
> > Cc: William Kucharski <william.kuchar...@oracle.com>
> > Cc: Andrew Morton <a...@linux-foundation.org>
> > Signed-off-by: Song Liu <songliubrav...@fb.com>
> 
> Acked-by: Johannes Weiner <han...@cmpxchg.org>

We should also be able to remove the unlocked tests for those two
conditions, right?

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 0a1b4b484ac5..a3ef6ce86bfa 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1601,17 +1601,6 @@ static void collapse_file(struct mm_struct *mm,
                                        result = SCAN_FAIL;
                                        goto xa_unlocked;
                                }
-                       } else if (!PageUptodate(page)) {
-                               xas_unlock_irq(&xas);
-                               wait_on_page_locked(page);
-                               if (!trylock_page(page)) {
-                                       result = SCAN_PAGE_LOCK;
-                                       goto xa_unlocked;
-                               }
-                               get_page(page);
-                       } else if (PageDirty(page)) {
-                               result = SCAN_FAIL;
-                               goto xa_locked;
                        } else if (trylock_page(page)) {
                                get_page(page);
                                xas_unlock_irq(&xas);