lkml.org 
[lkml]   [2003]   [Jul]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: RFC on io-stalls patch
On Wed, Jul 16 2003, Andrea Arcangeli wrote:
> On Wed, Jul 16, 2003 at 03:21:39PM +0200, Jens Axboe wrote:
> > 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.
>
> and on the small boxes that will happen much less now since on the small
> boxes the biggest vm overhead could been generated by the uncontrolled
> size of the I/O queue that previously could grow as big as 32M.

That is true, however noone runs 32MB boxes anymore :). So I doubt that
would be the case.

--
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/

\
 
 \ /
  Last update: 2005-03-22 13:46    [W:0.121 / U:0.200 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site