Re: [PATCHv2 3/3] mm: Use updated pmdp_invalidate() inteface to track dirty/accessed bits
From: Aneesh Kumar K.V
Date: Fri Jun 16 2017 - 11:57:41 EST
On Friday 16 June 2017 06:51 PM, Kirill A. Shutemov wrote:
On Fri, Jun 16, 2017 at 05:01:30PM +0530, Aneesh Kumar K.V wrote:
"Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> writes:
This patch uses modifed pmdp_invalidate(), that return previous value of pmd,
to transfer dirty and accessed bits.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
fs/proc/task_mmu.c | 8 ++++----
mm/huge_memory.c | 29 ++++++++++++-----------------
2 files changed, 16 insertions(+), 21 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index f0c8b33d99b1..f2fc1ef5bba2 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
.....
@@ -1965,7 +1955,6 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
page_ref_add(page, HPAGE_PMD_NR - 1);
write = pmd_write(*pmd);
young = pmd_young(*pmd);
- dirty = pmd_dirty(*pmd);
soft_dirty = pmd_soft_dirty(*pmd);
pmdp_huge_split_prepare(vma, haddr, pmd);
@@ -1995,8 +1984,6 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
if (soft_dirty)
entry = pte_mksoft_dirty(entry);
}
- if (dirty)
- SetPageDirty(page + i);
pte = pte_offset_map(&_pmd, addr);
BUG_ON(!pte_none(*pte));
set_pte_at(mm, addr, pte, entry);
@@ -2045,7 +2032,15 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
* and finally we write the non-huge version of the pmd entry with
* pmd_populate.
*/
- pmdp_invalidate(vma, haddr, pmd);
+ old = pmdp_invalidate(vma, haddr, pmd);
+
+ /*
+ * Transfer dirty bit using value returned by pmd_invalidate() to be
+ * sure we don't race with CPU that can set the bit under us.
+ */
+ if (pmd_dirty(old))
+ SetPageDirty(page);
+
pmd_populate(mm, pmd, pgtable);
if (freeze) {
Can we invalidate the pmd early here ? ie, do pmdp_invalidate instead of
pmdp_huge_split_prepare() ?
I think we can. But it means we would block access to the page for longer
than it's necessary on most architectures. I guess it's not a bit deal.
Maybe as separate patch on top of this patchet? Aneesh, would you take
care of this?
Yes, I cam do that.
-aneesh