linux-kernel - [PATCH] mm: Fix to infinite churning of mlocked page

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Date:	Thu, 20 Aug 2009 08:55:44 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	linux-mm <linux-mm@...ck.org>, lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Lee Schermerhorn <lee.schermerhorn@...com>
Subject: [PATCH] mm: Fix to infinite churning of mlocked page

Mlocked page might lost the isolatation race.
It cause the page to clear PG_mlocked while it remains
in VM_LOCKED vma. It means it can be put [in]active list.
We can rescue it by try_to_unmap in shrink_page_list.

But now, As Wu Fengguang pointed out, vmscan have a bug.
If the page has PG_referenced, it can't reach try_to_unmap
in shrink_page_list but put into active list. If the page
is referenced repeatedly, it can remain [in]active list
without moving unevictable list.

This patch can fix it.

Reported-by: Wu Fengguang <fengguang.wu@...el.com>
Signed-off-by: Minchan Kim <minchan.kim@...il.com>
Cc: KOSAKI Motohiro <<kosaki.motohiro@...fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@...com>
Cc: Rik van Riel <riel@...hat.com>
---
 mm/rmap.c   |    1 +
 mm/vmscan.c |    9 +++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 7d6fe4e..28aafe2 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -363,6 +363,7 @@ static int page_referenced_one(struct page *page,
 	 */
 	if (vma->vm_flags & VM_LOCKED) {
 		*mapcount = 1;	/* break early from loop */
+		*vm_flags |= VM_LOCKED;
 		goto out_unmap;
 	}

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 00596b9..70a63c4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -630,9 +630,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,

 		referenced = page_referenced(page, 1,
 						sc->mem_cgroup, &vm_flags);
-		/* In active use or really unfreeable?  Activate it. */
+		/*
+		 * In active use or really unfreeable?  Activate it.
+		 * If page which have PG_mlocked lost isoltation race,
+		 * try_to_unmap moves it to unevictable list
+		 */
 		if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
-					referenced && page_mapping_inuse(page))
+					referenced && page_mapping_inuse(page)
+					&& !(vm_flags & VM_LOCKED))
 			goto activate_locked;

 		/*
--
1.5.4.3


-- 
Kind regards,
Minchan Kim
--
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