[PATCH v2] fix mlocked page counter mistmatch

MinChan Kim
2009-02-03T04:24:35Z

When I tested following program, I found that mlocked counter
is strange.
It couldn't free some mlocked pages of test program.
It is caused that try_to_unmap_file don't check real
page mapping in vmas.

That's because goal of address_space for file is to find all processes
into which the file's specific interval is mapped.
What I mean is that it's not related page but file's interval.

Even if the page isn't really mapping at the vma, it returns
SWAP_MLOCK since the vma have VM_LOCKED, then calls
try_to_mlock_page. After all, mlocked counter is increased again.

COWed anon page in a file-backed vma could be a such case.
This patch resolves it.

This patch is based on 2.6.28-rc2-mm1.

-- my test program --

int main()
{
mlockall(MCL_CURRENT);
return 0;
}

-- before --

root@barrios-target-linux:~# cat /proc/meminfo | egrep 'Mlo|Unev'
Unevictable: 0 kB
Mlocked: 0 kB

-- after --

root@barrios-target-linux:~# cat /proc/meminfo | egrep 'Mlo|Unev'
Unevictable: 8 kB
Mlocked: 8 kB

Signed-off-by: MinChan Kim <minchan.kim@gmail.com>
Acked-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Tested-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

---
mm/rmap.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 1099394..bd24b55 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1080,7 +1080,8 @@ static int try_to_unmap_file(struct page *page, int unlock, int migration)
spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
if (MLOCK_PAGES && unlikely(unlock)) {
- if (!(vma->vm_flags & VM_LOCKED))
+ if (!((vma->vm_flags & VM_LOCKED) &&
+ page_mapped_in_vma(page, vma)))
continue; /* must visit all vmas */
ret = SWAP_MLOCK;
} else {
--
1.5.4.3

--
Kinds Regards
MinChan Kim