Re: [PATCH 2/3] page allocator: Do not allow interrupts to use ALLOC_HARDER

Pavel Machek
2009-10-31T20:12:07Z

On Sat 2009-10-31 12:51:14, David Rientjes wrote:
> On Sat, 31 Oct 2009, Pavel Machek wrote:
>
> > > Giving rt tasks access to memory reserves is necessary to reduce latency,
> > > the privilege does not apply to interrupts that subsequently get run on
> > > the same cpu.
> >
> > If rt task needs to allocate memory like that, then its broken,
> > anyway...
>
> Um, no, it's a matter of the kernel implementation. We allow such tasks
> to allocate deeper into reserves to avoid the page allocator from
> incurring a significant penalty when direct reclaim is required.
> Background reclaim has already commenced at this point in the
>slowpath.

But we can't guarantee that enough memory will be ready in the
reserves. So if realtime task relies on it, it is broken, and will
fail to meet its deadlines from time to time.
Pavel
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