Re: [PATCH] mm: Warn once when a page is freed with PG_mlocked set (resend)

[Johannes Weiner <hannes@cmpxchg.org>]

Hello Mel,

On Wed, Jul 15, 2009 at 11:48:34AM +0100, Mel Gorman wrote:
> 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 |   16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index caa9268..f8902e7 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -495,8 +495,16 @@ 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)
> +{
> +	if (unlikely(wasMlocked)) {
> +		WARN_ONCE(1, 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);

Since the warning is the only action in this branch, wouldn't
WARN_ONCE(wasMlocked, KERN_WARNING ...) be better?

	Hannes