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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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