* KOSAKI Motohiro <kosaki.motoh...@jp.fujitsu.com> [2011-04-01 22:21:26]:
> > * KOSAKI Motohiro <kosaki.motoh...@jp.fujitsu.com> [2011-04-01 16:56:57]:
> >
> > > Hi
> > >
> > > > > 1) zone reclaim doesn't work if the system has multiple node and the
> > > > > workload is file cache oriented (eg file server, web server, mail
> > > > > server, et al).
> > > > > because zone recliam make some much free pages than
> > > > > zone->pages_min and
> > > > > then new page cache request consume nearest node memory and then it
> > > > > bring next zone reclaim. Then, memory utilization is reduced and
> > > > > unnecessary LRU discard is increased dramatically.
> > > > >
> > > > > SGI folks added CPUSET specific solution in past.
> > > > > (cpuset.memory_spread_page)
> > > > > But global recliam still have its issue. zone recliam is HPC
> > > > > workload specific
> > > > > feature and HPC folks has no motivation to don't use CPUSET.
> > > >
> > > > I am afraid you misread the patches and the intent. The intent to
> > > > explictly enable control of unmapped pages and has nothing
> > > > specifically to do with multiple nodes at this point. The control is
> > > > system wide and carefully enabled by the administrator.
> > >
> > > Hm. OK, I may misread.
> > > Can you please explain the reason why de-duplication feature need to
> > > selectable and
> > > disabled by defaut. "explicity enable" mean this feature want to spot
> > > corner case issue??
> >
> > Yes, because given a selection of choices (including what you
> > mentioned in the review), it would be nice to have
> > this selectable.
>
> It's no good answer. :-/
I am afraid I cannot please you with my answers
> Who need the feature and who shouldn't use it? It this enough valuable for
> enough large
> people? That's my question point.
>
You can see the use cases documented, including when running Linux as
a guest under other hypervisors, today we have a choice of not using
host page cache with cache=none, but nothing the other way round.
There are other use cases for embedded folks (in terms of controlling
unmapped page cache), please see previous discussions.
--
Three Cheers,
Balbir
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