linux-kernel - [PATCH] fix mlocked page counter mismatch

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Date:	Mon, 2 Feb 2009 15:16:22 +0900
From:	MinChan Kim <minchan.kim@...il.com>
To:	linux mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux kernel <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
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@...rios-target-linux:~# cat /proc/meminfo | egrep 'Mlo|Unev'
Unevictable:           0 kB
Mlocked:               0 kB

-- after --

root@...rios-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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