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Re: Autotuning of kern.ipc.shmmaxpgs

On Mon, 23 Feb 2009, Joerg Sonnenberger wrote:

On Mon, Feb 23, 2009 at 02:56:49PM +0000, Mindaugas Rasiukevicius wrote:
Joerg Sonnenberger <> wrote:
currently the maximum size of SysV shared memory is limited by a static
MD limit. The attached patch allows platforms to not specify such a
limit. If the kernel config doesn't specify one either, the kernel will
compute a limit on startup based on physmem. Platforms with limited KVA
can also set SHMMAX_AUTO_LIMIT, which places an upper boundary on the
auto-tuned value.

- I tend to think that removing MD definitions of SHMMAXPGS (or SHMMAX)
  would be the right thing to do.

In general: yes.

- Why do you think KVA is the issue here?

It is the only reason I can find for having a MD limit at all. If it is
not considered an issue on things like VAX which can't grow the kernel
map, I'm all for removing the static limits completely. Given that the
shared memory segments are directly attached to to the process's vmmap,
it should be irrelevant here.

        Would there be any sense in writing a test program to try to
        allocate as much SysV shared memory s possible, then get someone
        to test it as a non root user on a vax with the static limit
        completely removed. If it doesn't choke, then nuke the static
        limit altogether, otherwise maybe keep it as a MD define, but
        default it unset for everything and let ports set it if they
        find they need it (maybe add the test to atf).

                David/absolute       -- No hype required --

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