Re: [PATCH 05/17] writeback: quit throttling when signal pending

[Wu Fengguang <fengguang.wu@intel.com>]

On Tue, Sep 14, 2010 at 04:23:56PM +0800, KOSAKI Motohiro wrote:
> > Subject: writeback: quit throttling when fatal signal pending
> > From: Wu Fengguang <fengguang.wu@intel.com>
> > Date: Wed Sep 08 17:40:22 CST 2010
> > 
> > This allows quick response to Ctrl-C etc. for impatient users.
> > 
> > It mainly helps the rare bdi/global dirty exceeded cases.
> > In the normal case of not exceeded, it will quit the loop anyway. 
> > 
> > CC: Neil Brown <neilb@suse.de>
> > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> > ---
> >  mm/page-writeback.c |    3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > --- linux-next.orig/mm/page-writeback.c	2010-09-12 13:25:23.000000000 +0800
> > +++ linux-next/mm/page-writeback.c	2010-09-13 11:39:33.000000000 +0800
> > @@ -552,6 +552,9 @@ static void balance_dirty_pages(struct a
> >  		__set_current_state(TASK_INTERRUPTIBLE);
> >  		io_schedule_timeout(pause);
> >  
> > +		if (fatal_signal_pending(current))
> > +			break;
> > +
> >  check_exceeded:
> >  		/*
> >  		 * The bdi thresh is somehow "soft" limit derived from the
> 
> I think we need to change callers (e.g. generic_perform_write) too.
> Otherwise, plenty write + SIGKILL combination easily exceed dirty limit.
> It mean we can see strange OOM.

If it's dangerous, we can do without this patch.  The users can still
get quick response in normal case after all.

However, I suspect the process is guaranteed to exit on
fatal_signal_pending, so it won't dirty more pages :)

Thanks,
Fengguang