|| ||Andrew Morton <akpm-AT-linux-foundation.org>|
|| ||Rik van Riel <riel-AT-redhat.com>|
|| ||Re: The performance and behaviour of the anti-fragmentation related
|| ||Fri, 2 Mar 2007 14:59:06 -0800|
|| ||Bill Irwin <bill.irwin-AT-oracle.com>,
Christoph Lameter <clameter-AT-engr.sgi.com>,
Mel Gorman <mel-AT-skynet.ie>, npiggin-AT-suse.de, mingo-AT-elte.hu,
On Fri, 02 Mar 2007 17:34:31 -0500
Rik van Riel <email@example.com> wrote:
> >>>> The main reason they end up pounding the LRU locks is the
> >>>> swappiness heuristic. They scan too much before deciding
> >>>> that it would be a good idea to actually swap something
> >>>> out, and with 32 CPUs doing such scanning simultaneously...
> >>> What kernel version?
> >> Customers are on the 2.6.9 based RHEL4 kernel, but I believe
> >> we have reproduced the problem on 2.6.18 too during stress
> >> tests.
> > The prev_priority fixes were post-2.6.18
> We tested them. They only alleviate the problem slightly in
> good situations, but things still fall apart badly with less
> friendly workloads.
What is it with vendors finding MM problems and either not fixing them or
kludging around them and not telling the upstream maintainers about *any*
> >> I have no reason to believe we should stick our heads in the
> >> sand and pretend it no longer exists on 2.6.21.
> > I have no reason to believe anything. All I see is handwaviness,
> > speculation and grand plans to rewrite vast amounts of stuff without even a
> > testcase to demonstrate that said rewrite improved anything.
> Your attitude is exactly why the VM keeps falling apart over
> and over again.
> Fixing "a testcase" in the VM tends to introduce problems for
> other test cases, ad infinitum.
In that case it was a bad fix. The aim is to fix known problems without
introducing regressions in other areas. A perfectly legitimate approach.
You seem to be saying that we'd be worse off if we actually had a testcase.
> There's a reason we end up
> fixing the same bugs over and over again.
No we don't.
> I have been looking through a few hundred VM related bugzillas
> and have found the same bugs persist over many different
> versions of Linux, sometimes temporarily fixed, but they seem
> to always come back eventually...
> > None of this is going anywhere, is is it?
> I will test my changes before I send them to you, but I cannot
> promise you that you'll have the computers or software needed
> to reproduce the problems. I doubt I'll have full time access
> to such systems myself, either.
> 32GB is pretty much the minimum size to reproduce some of these
> problems. Some workloads may need larger systems to easily trigger
32GB isn't particularly large.
Somehow I don't believe that a person or organisation which is incapable of
preparing even a simple testcase will be capable of fixing problems such as
this without breaking things.
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