mm: softdirty: make freshly remapped file pages being softdirty unconditionally

Hugh reported:

 | I noticed your soft_dirty work in install_file_pte(): which looked
 | good at first, until I realized that it's propagating the soft_dirty
 | of a pte it's about to zap completely, to the unrelated entry it's
 | about to insert in its place.  Which seems very odd to me.

Indeed this code ends up being nop in result -- pte_file_mksoft_dirty()
operates with pte_t argument and returns new pte_t which were never used
after.  After looking more I think what we need is to soft-dirtify all
newely remapped file pages because it should look like a new mapping for
memory tracker.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reported-by: Hugh Dickins <hughd@google.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/fremap.c b/mm/fremap.c
index 34feba6..2c5646f 100644 (file)
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -82,13 +82,10 @@ static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
 
        ptfile = pgoff_to_pte(pgoff);
 
-       if (!pte_none(*pte)) {
-               if (pte_present(*pte) && pte_soft_dirty(*pte))
-                       pte_file_mksoft_dirty(ptfile);
+       if (!pte_none(*pte))
                zap_pte(mm, vma, addr, pte);
-       }
 
-       set_pte_at(mm, addr, pte, ptfile);
+       set_pte_at(mm, addr, pte, pte_file_mksoft_dirty(ptfile));
        /*
         * We don't need to run update_mmu_cache() here because the "file pte"
         * being installed by install_file_pte() is not a real pte - it's a