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SubjectRe: [PATCH] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous
On Tue, May 31, 2011 at 11:38:30PM +0900, Minchan Kim wrote:
> > Yes. You find a new BUG.
> > It seems to be related to this problem but it should be solved although
>
> typo : It doesn't seem to be.

This should fix it, but I doubt it matters for this problem.

===
Subject: mm: no page_count without a page pin

From: Andrea Arcangeli <aarcange@redhat.com>

It's unsafe to run page_count during the physical pfn scan.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index faa0a08..e41e78a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1124,8 +1124,18 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
nr_lumpy_dirty++;
scan++;
} else {
- /* the page is freed already. */
- if (!page_count(cursor_page))
+ /*
+ * We can't use page_count() as that
+ * requires compound_head and we don't
+ * have a pin on the page here. If a
+ * page is tail, we may or may not
+ * have isolated the head, so assume
+ * it's not free, it'd be tricky to
+ * track the head status without a
+ * page pin.
+ */
+ if (!PageTail(cursor_page) &&
+ !atomic_read(&cursor_page->_count))
continue;
break;
}

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