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authorAndrea Arcangeli <aarcange@redhat.com>2011-03-11 14:58:29 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-13 15:35:57 -0700
commit2da28bfd9665f49d40abb4c7720b43135feaf79a (patch)
tree5bdefc06aab34b5dd35e479e7d7966ea30275335
parent78f9bbb5a6f41fcb7934848c7821b99718f7e338 (diff)
thp: fix page_referenced to modify mapcount/vm_flags only if page is found
When vmscan.c calls page_referenced(), if an anon page was created before a process forked, rmap will search for it in both of the processes, even though one of them might have since broken COW. If the child process mlocks the vma where the COWed page belongs to, page_referenced() running on the page mapped by the parent would lead to *vm_flags getting VM_LOCKED set erroneously (leading to the references on the parent page being ignored and evicting the parent page too early). *mapcount would also be decremented by page_referenced_one even if the page wasn't found by page_check_address. This also lets pmdp_clear_flush_young_notify() go ahead on a pmd_trans_splitting() pmd. We hold the page_table_lock so __split_huge_page_map() must wait the pmdp_clear_flush_young_notify() to complete before it can modify the pmd. The pmd is also still mapped in userland so the young bit may materialize through a tlb miss before split_huge_page_map runs. This will provide a more accurate page_referenced() behavior during split_huge_page(). Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reported-by: Michel Lespinasse <walken@google.com> Reviewed-by: Michel Lespinasse <walken@google.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Reviewed-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Rik van Riel<riel@redhat.com> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/rmap.c54
1 files changed, 35 insertions, 19 deletions
diff --git a/mm/rmap.c b/mm/rmap.c
index f21f4a1d6a1..941bf82e896 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -497,41 +497,51 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
struct mm_struct *mm = vma->vm_mm;
int referenced = 0;
- /*
- * Don't want to elevate referenced for mlocked page that gets this far,
- * in order that it progresses to try_to_unmap and is moved to the
- * unevictable list.
- */
- if (vma->vm_flags & VM_LOCKED) {
- *mapcount = 0; /* break early from loop */
- *vm_flags |= VM_LOCKED;
- goto out;
- }
-
- /* Pretend the page is referenced if the task has the
- swap token and is in the middle of a page fault. */
- if (mm != current->mm && has_swap_token(mm) &&
- rwsem_is_locked(&mm->mmap_sem))
- referenced++;
-
if (unlikely(PageTransHuge(page))) {
pmd_t *pmd;
spin_lock(&mm->page_table_lock);
+ /*
+ * rmap might return false positives; we must filter
+ * these out using page_check_address_pmd().
+ */
pmd = page_check_address_pmd(page, mm, address,
PAGE_CHECK_ADDRESS_PMD_FLAG);
- if (pmd && !pmd_trans_splitting(*pmd) &&
- pmdp_clear_flush_young_notify(vma, address, pmd))
+ if (!pmd) {
+ spin_unlock(&mm->page_table_lock);
+ goto out;
+ }
+
+ if (vma->vm_flags & VM_LOCKED) {
+ spin_unlock(&mm->page_table_lock);
+ *mapcount = 0; /* break early from loop */
+ *vm_flags |= VM_LOCKED;
+ goto out;
+ }
+
+ /* go ahead even if the pmd is pmd_trans_splitting() */
+ if (pmdp_clear_flush_young_notify(vma, address, pmd))
referenced++;
spin_unlock(&mm->page_table_lock);
} else {
pte_t *pte;
spinlock_t *ptl;
+ /*
+ * rmap might return false positives; we must filter
+ * these out using page_check_address().
+ */
pte = page_check_address(page, mm, address, &ptl, 0);
if (!pte)
goto out;
+ if (vma->vm_flags & VM_LOCKED) {
+ pte_unmap_unlock(pte, ptl);
+ *mapcount = 0; /* break early from loop */
+ *vm_flags |= VM_LOCKED;
+ goto out;
+ }
+
if (ptep_clear_flush_young_notify(vma, address, pte)) {
/*
* Don't treat a reference through a sequentially read
@@ -546,6 +556,12 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
pte_unmap_unlock(pte, ptl);
}
+ /* Pretend the page is referenced if the task has the
+ swap token and is in the middle of a page fault. */
+ if (mm != current->mm && has_swap_token(mm) &&
+ rwsem_is_locked(&mm->mmap_sem))
+ referenced++;
+
(*mapcount)--;
if (referenced)