Re: Getting rid of SHMMAX/SHMALL ?

[Andi Kleen <ak@suse.de>]

On Thu, Aug 04, 2005 at 03:49:37PM -0700, Chen, Kenneth W wrote:
> Andi Kleen wrote on Thursday, August 04, 2005 6:24 AM
> > I think we should just get rid of the per process limit and keep
> > the global limit, but make it auto tuning based on available memory.
> > That is still not very nice because that would likely keep it < available 
> > memory/2, but I suspect databases usually want more than that. So
> > I would even make it bigger than tmpfs for reasonably big machines.
> > Let's say
> > 
> > if (main memory >= 1GB)
> > 	maxmem = main memory - main memory/8 
> 
> This might be too low on large system.  We usually stress shm pretty hard
> for db application and usually use more than 87% of total memory in just
> one shm segment.  So I prefer either no limit or a tunable.

With large system you mean >32GB right?

I think on a large systems some tuning is reasonable because they likely
have trained admins. I'm more worried on reasonable defaults for the
class of systems with 0-4GB

The /8 was to account for the overhead of page tables and mem_map and
leave some other memory for the system, but you're right it might be less 
with hugetlbfs.

-Andi
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