linux-kernel - [PATCH v2] fix mlocked page counter mistmatch

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Message-ID: <20090203042405.GB16179@barrios-desktop>
Date:	Tue, 3 Feb 2009 13:24:05 +0900
From:	MinChan Kim <minchan.kim@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	linux mm <linux-mm@...ck.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>
Subject: [PATCH v2] fix mlocked page counter mistmatch


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@...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

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

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