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Subject[PATCH] fix mlocked page counter mismatch
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.

This patch is based on 2.6.28-rc2-mm1.

-- my test program --

#include <stdio.h>
#include <sys/mman.h>
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


--

diff --git a/mm/rmap.c b/mm/rmap.c
index 1099394..9ba1fdf 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1073,6 +1073,9 @@ static int try_to_unmap_file(struct page *page, int unlock, int migration)
unsigned long max_nl_size = 0;
unsigned int mapcount;
unsigned int mlocked = 0;
+ unsigned long address;
+ pte_t *pte;
+ spinlock_t *ptl;

if (MLOCK_PAGES && unlikely(unlock))
ret = SWAP_SUCCESS; /* default for try_to_munlock() */
@@ -1089,6 +1092,13 @@ static int try_to_unmap_file(struct page *page, int unlock, int migration)
goto out;
}
if (ret == SWAP_MLOCK) {
+ address = vma_address(page, vma);
+ if (address != -EFAULT) {
+ pte = page_check_address(page, vma->vm_mm, address, &ptl, 0);
+ if (!pte)
+ continue;
+ pte_unmap_unlock(pte, ptl);
+ }
mlocked = try_to_mlock_page(page, vma);
if (mlocked)
break; /* stop if actually mlocked page */


--
Kinds Regards
MinChan Kim



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