Re: 4g/4g for 2.6.6

Andrea Arcangeli
2004-05-25T19:42:48Z

On Tue, May 25, 2004 at 03:15:14PM -0400, Rik van Riel wrote:
> On Mon, 24 May 2004, Andrea Arcangeli wrote:
> > On Mon, May 24, 2004 at 10:25:22AM +0200, Ingo Molnar wrote:
> > > on how quickly 'x86 with more than 4GB of RAM' and
> >
> > s/4GB/32GB/
> >
> > my usual x86 test box has 48G of ram (though to keep an huge margin of
> > safety we assume 32G is the very safe limit).
>
> Just how many 3GB sized processes can you run on that
> system, if each of them have a hundred or so VMAs ?

with 400m of normal zone we can allocate 5000000 vmas, if each task uses
100 of them that's around 50000 processes. The 3G size doesn't matter.

I think you meant each task using some _dozen_thousand_ of vmas (not
hundreds), that's what actually happens with 32k large vmas spread over
2G of shared memory on some database (assuming no merging, with merging
it goes down to the few thousands), but remap_file_pages has been
designed exactly to avoid allocating several thousands of VMA per task,
no? So it's just 1 vma per task (plus a few more vmas for the binary
shared libs and anonymous memory).

Clearly by opening enough files or enough network sockets or enough vmas
or similar, you can still run out of normal zone, even on a 2G system,
but this is not the point or you would be shipping 4:4 on the 2G systems
too, no? We're not trying to make it impossible to run out of zone
normal, even 4:4 can't make that impossible to happen on >4G boxes.