Re: Linux max on shared buffers?

Is it significant that you these shared libraries remain mapped for the
duration of the process, while blocks are moved in and out?

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Curt Sampson wrote:
> On Tue, 23 Jul 2002, Jan Wieck wrote:
>
> > No resource limit on that? So my 200 backends all map some random
> > 16,000 blocks from 400 files and the kernel jiggles with it like
> > it's never did anything else?
>
> Do you know how much of your process is already mmaped in exactly this
> way? If you take a look at the source code for ld.so, you'll likely find
> that all of the shared libraries your executable is using are mapped
> in to your process space with mmap. And in fact, it's all mmap under
> the hood as well; the kernel is effectively internal calls to mmap to
> map the executable and ld.so into memory in the first place. On BSD
> systems, at least, but probably others, all of the shared memory is just
> an anonymous (i.e., using swap space as the backing store) bunch of
> mmapped pages.
>
> So in theory, having several hundred processes each with a gigabyte
> or two of mmaped 8K blocks is not going to be a problem. However,
> I've not tested this in practice (though I will do so one day) so
> that's not to say it won't fail on certain OSes. In that case you'd
> want to map much smaller amounts, and live with the extra syscall
> overhead. But even so, it would still be far more efficient than
> copying blocks into and out of shared memory.
>
> cjs
> --
> Curt Sampson <cjs(at)cynic(dot)net> +81 90 7737 2974 http://www.netbsd.org
> Don't you know, in this new Dark Age, we're all light. --XTC
>
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