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Subject[PATCH] mm: Warn once when a page is freed with PG_mlocked set V2
Changelog since V1
o Remove unnecessary branch

When a page is freed with the PG_mlocked set, it is considered an unexpected
but recoverable situation. A counter records how often this event happens
but it is easy to miss that this event has occured at all. This patch warns
once when PG_mlocked is set to prompt debuggers to check the counter to
see how often it is happening.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
---
mm/page_alloc.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index caa9268..97c8ecf 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -495,8 +495,14 @@ static inline void free_page_mlock(struct page *page)
static void free_page_mlock(struct page *page) { }
#endif

-static inline int free_pages_check(struct page *page)
+static inline int free_pages_check(struct page *page, int wasMlocked)
{
+ WARN_ONCE(wasMlocked, KERN_WARNING
+ "Page flag mlocked set for process %s at pfn:%05lx\n"
+ "page:%p flags:0x%lX\n",
+ current->comm, page_to_pfn(page),
+ page, page->flags|__PG_MLOCKED);
+
if (unlikely(page_mapcount(page) |
(page->mapping != NULL) |
(atomic_read(&page->_count) != 0) |
@@ -562,7 +568,7 @@ static void __free_pages_ok(struct page *page, unsigned int order)
kmemcheck_free_shadow(page, order);

for (i = 0 ; i < (1 << order) ; ++i)
- bad += free_pages_check(page + i);
+ bad += free_pages_check(page + i, wasMlocked);
if (bad)
return;

@@ -1027,7 +1033,7 @@ static void free_hot_cold_page(struct page *page, int cold)

if (PageAnon(page))
page->mapping = NULL;
- if (free_pages_check(page))
+ if (free_pages_check(page, wasMlocked))
return;

if (!PageHighMem(page)) {

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