Re: The performance and behaviour of the anti-fragmentation related patches

[Rik van Riel <riel@redhat.com>]

Andrew Morton wrote:
> On Fri, 02 Mar 2007 16:19:19 -0500
> Rik van Riel <riel@redhat.com> wrote:
>> Bill Irwin wrote:
>>> On Fri, Mar 02, 2007 at 01:23:28PM -0500, Rik van Riel wrote:
>>>> With 32 CPUs diving into the page reclaim simultaneously,
>>>> each trying to scan a fraction of memory, this is disastrous
>>>> for performance.  A 256GB system should be even worse.
>>> Thundering herds of a sort pounding the LRU locks from direct reclaim
>>> have set off the NMI oopser for users here.
>> Ditto here.
> 
> Opterons?

It's happened on IA64, too.  Probably on Intel x86-64 as well.

>> 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.

I have no reason to believe we should stick our heads in the
sand and pretend it no longer exists on 2.6.21.

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