On 13.11.2004, at 08:48, Manish Singh wrote:

shm is a special case. I'm talking about allocating highmem

So, what is the userspace API for this?

AFAIK there's no direct userspace helper to address highmem segments; one can only map them in the Linux kernel and provide them to userspace (or not).[1] Since this does not lead to any particular improvement for userspace, without having a patched kernel, it does at least have the advantage of buffers in the kernel to be allocated from highmem first.

If you need to address more than the typical limits (1, 2
or 3 GiB) per process, you will need to write a kernel
module that communicates with userspace through some syscall
or device.

In case you want to see some real improvement, have a look
at [2] which contains an (probably outdated) patch to have
a real 4 GiB available for userspace.

[1] http://www.skynet.ie/%7Emel/projects/vm/guide/html/understand/ understand-html.html, chapters 3.4 and 10.
[2] http://lwn.net/Articles/39283/


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