Re: [PATCH] Warn if we run out of swap space

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 22 May 2009 14:58:19 -0400 (EDT) Christoph Lameter <cl@linux-foundation.org> wrote:

> 
> Subject: Warn if we run out of swap space
> 
> Running out of swap space means that the evicton of anonymous pages may no longer
> be possible which can lead to OOM conditions.
> 
> Print a warning when swap space first becomes exhausted.
> 
> Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
> 
> ---
>  mm/swapfile.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> Index: linux-2.6/mm/swapfile.c
> ===================================================================
> --- linux-2.6.orig/mm/swapfile.c	2009-05-22 12:25:19.000000000 -0500
> +++ linux-2.6/mm/swapfile.c	2009-05-22 13:56:10.000000000 -0500
> @@ -380,6 +380,7 @@ swp_entry_t get_swap_page(void)
>  	pgoff_t offset;
>  	int type, next;
>  	int wrapped = 0;
> +	static int printed = 0;
> 
>  	spin_lock(&swap_lock);
>  	if (nr_swap_pages <= 0)
> @@ -410,6 +411,10 @@ swp_entry_t get_swap_page(void)
>  	}
> 
>  	nr_swap_pages++;
> +	if (!printed) {
> +		printed = 1;
> +		printk(KERN_WARNING "All of swap is in use. Some pages cannot be swapped out.");
> +	}
>  noswap:
>  	spin_unlock(&swap_lock);
>  	return (swp_entry_t) {0};

I think the warning is useful.  (Although the missing \n makes me wonder
how well tested this is).

However the once-per-boot thing weakens it quite a lot.  Suppose someone
runs out of swap, sees the message, adds more swap then later runs out
again?

Perhaps we could clear the `printed' flag each time the amount of online
swap is altered?

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