On Wed, Jul 16 2003, Andrea Arcangeli wrote:
> On Wed, Jul 16, 2003 at 03:04:42PM +0200, Jens Axboe wrote:
> > On Wed, Jul 16 2003, Andrea Arcangeli wrote:
> > > On Wed, Jul 16, 2003 at 02:46:56PM +0200, Jens Axboe wrote:
> > > > Well it's a combined problem. Threshold too high on dirty memory,
> > > > someone doing a read well get stuck flushing out as well.
> > >
> > > a pure read not. the write throttling should be per-process, then there
> > > will be little risk.
> >
> > A read from user space, dirtying data along the way.
>
> it doesn't necessairly block on dirty memory. We even _free_ ram clean
> if needed, exactly because of that. You can raise the amount of _free_
> ram up to 99% of the whole ram in your box to be almost guaranteed to
> never wait on dirty memory freeing. Of course the default tries to
> optimize for writeback cache and there's a reasonable margin to avoid
> writing dirty stuff. the sysctl is there for special usages where you
> want to never block in a read from userspace regardless whatever the
> state of the system.
That may be so, but no user will ever touch that sysctl. He just
experiences what Alan outlined, system grinds to a complete halt. Only
much later does it get going again.
-- Jens Axboe- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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