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SubjectRe: RFC on io-stalls patch
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.

Andrea
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