On 05/01/2014 10:44 AM, Mel Gorman wrote:
When adding pages to the LRU we clear the active bit unconditionally. As the
page could be reachable from other paths we cannot use unlocked operations
without risk of corruption such as a parallel mark_page_accessed. This
patch test if is necessary to clear the atomic flag before using an atomic
active
operation. In the unlikely even this races with mark_page_accesssed the
consequences are simply that the page may be promoted to the active list
that might have been left on the inactive list before the patch. This is
a marginal consequence.
Well if this is racy, then even before the patch, mark_page_accessed
might have come right after ClearPageActive(page) anyway? Or is the
changelog saying that this change only extended the race window that
already existed? If yes it could be more explicit, as now it might sound
as if the race was introduced.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
include/linux/swap.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index da8a250..395dcab 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -329,13 +329,15 @@ extern void add_page_to_unevictable_list(struct page *page);
*/
static inline void lru_cache_add_anon(struct page *page)
{
- ClearPageActive(page);
+ if (PageActive(page))
+ ClearPageActive(page);
__lru_cache_add(page);
}
static inline void lru_cache_add_file(struct page *page)
{
- ClearPageActive(page);
+ if (PageActive(page))
+ ClearPageActive(page);
__lru_cache_add(page);
}
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