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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Fri, 22 May 2009 21:38:47 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> 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?
> 
How about clearing it in the condition vm_swap_full() returns false ?
Anyway, I welcome this patch :)

Thanks,
-Kame

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>