Re: [PATCH -mm v8 4/7] proc: add kpagecgroup file

[Vladimir Davydov <vdavydov-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>]

On Thu, Jul 16, 2015 at 12:04:59PM -0700, Andres Lagar-Cavilla wrote:
> On Thu, Jul 16, 2015 at 2:28 AM, Vladimir Davydov <vdavydov-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
> wrote:
> 
> > On Wed, Jul 15, 2015 at 12:03:18PM -0700, Andres Lagar-Cavilla wrote:
> > > For both /proc/kpage* interfaces you add (and more critically for the
> > > rmap-causing one, kpageidle):
> > >
> > > It's a good idea to do cond_sched(). Whether after each pfn, each Nth
> > > pfn, each put_user, I leave to you, but a reasonable cadence is
> > > needed, because user-space can call this on the entire physical
> > > address space, and that's a lot of work to do without re-scheduling.
> >
> > I really don't think it's necessary. These files can only be
> > read/written by the root, who has plenty ways to kill the system anyway.
> > The program that is allowed to read/write these files must be conscious
> > and do it in batches of reasonable size. AFAICS the same reasoning
> > already lays behind /proc/kpagecount and /proc/kpageflag, which also do
> > not thrust the "right" batch size on their readers.
> >
> 
> Beg to disagree. You're conflating intended use with system health. A
> cond_sched() is a one-liner.

I would still prefer not to clutter the code with cond_resched's, but I
don't think it's a matter worth arguing upon, so I'll prepare a patch
that makes all /proc/kapge* files issue cond_resched periodically and
leave it up to Andrew to decide if it should be applied or not.

Thanks,
Vladimir