[patch 1/4] mm: Make freshly remapped file pages being softdirty unconditionally

Cyrill Gorcunov
2014-03-24T13:00:49Z

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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.

Reported-by: Hugh Dickins <hughd@google.com>
CC: Pavel Emelyanov <xemul@parallels.com>
CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
---
mm/fremap.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

Index: linux-2.6.git/mm/fremap.c
===================================================================
--- linux-2.6.git.orig/mm/fremap.c
+++ linux-2.6.git/mm/fremap.c
@@ -66,13 +66,10 @@ static int install_file_pte(struct mm_st

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