On Thu, Jul 16, 2015 at 2:28 AM, Vladimir Davydov <vdavydov@parallels.com>
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.

Andres

>
> Thanks,
> Vladimir
>



-- 
Andres Lagar-Cavilla | Google Kernel Team | andreslc@google.com