Bryan J. Smith wrote:
On Mon, 2006-06-12 at 14:35 +0200, Per Jessen wrote:
But we are talking about an application accessing memory, which on Linux is done exclusively through the virtual memory manager. That the VMM will use the PAE for addressing up to 64Gb of physical memory does not concern the application.
But how does the 32-bit application use its pointers to access and differentiate more than 4GiB?
That was never really the topic of this thread - presumably it's through use of some as-of-yet-unknown PAE API.
I think people keep confusing the difference between "total userspace" among _all_ applications and "total userspace" used by *1* application.
That's certainly possible. Right from the beginning of this thread I've said the application address does not change, but remains at 4Gb. And that someone running non-PAE-aware applications may perfectly well benefit from running on a PAE-aware operating system such as Linux (when built with CONFIG_HIGHMEM64G). In summary - the application does not need to know about PAE to use memory addressed through PAE.
OK - do you know how this is done on Linux? I'm really curious as I've always considered this kernel-only stuff. I have no problem with the concept of mapping physical memory (normally not used by the kernel) into my own address-space, I just did not think Linux provided that option.
Oracle uses it.
Do you know what "it" is? I wonder if "it" is an option for mysql and maxdb too?
My understanding of Linux' use of PAE is that enabling CONFIG_HIGHMEM64 essentially makes the kernel switch to a three-level instead of a two-level address lookup.
That's another story.
Well, if we exclude applications using the unknown PAE API, isn't the above really the _whole_ story?
You can't just do a "malloc" on x86 Linux and get more than 4GiB.
My point exactly. But I'm still interested in how it's done. /Per Jessen, Zürich -- Check the headers for your unsubscription address For additional commands send e-mail to suse-linux-e-help@suse.com Also check the archives at http://lists.suse.com Please read the FAQs: suse-linux-e-faq@suse.com