Re: Large Shared Memory

Matti Aarnio (matti.aarnio@sonera.fi)
Wed, 30 Jun 1999 21:55:23 +0300

On Wed, Jun 30, 1999 at 12:48:52PM -0400, Bret Orsburn wrote:
> Worthies of the Linux Kernel List:
>
> I need to create a rather large region of shared memory -- on the order of 50MB.
> More specifically, I need a contiguous region of memory that can be mapped into
> multiple processes (serially, not simultaneously) on a uniprocessor system and
> persist beyond any particular process.
>
> It appears that there is a limit on System V style shared memory segments of
> about 4MB, so that method is out.

(This is a FAQ with e.g. Oracle setup at Linux..)

Size of the SysV SHM is runtime controlled by writing to:
/proc/sys/kernel/shmmax

# echo "55000000" > /proc/sys/kernel/shmmax

Now your maximum SHM size is 55 million bytes (you get the idea ?)

There are some limits at how high you can push that, but they
are pretty high... At least 512 MB is possible at SysV SHM.

> Is there a Right Way to do this with the 2.2 kernel?
>
> Thanks.
> ----
> Bret Orsburn
> borsburn@codonics.com

/Matti Aarnio <matti.aarnio@sonera.fi>

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