Ingo Molnar wrote:
originally i tested this feature with some minimal amount of RAM
simulated by UML 128MB or so. That's just 32 thousand pages, but still
the improvement was massive: context-switch times in UML were cut in
half or more. Process-creation times improved 10-fold. With this feature
included I accidentally (for the first time ever!) confused an UML shell
prompt with a real shell prompt. (before that UML was so slow [even in
"skas mode"] that you'd immediately notice it by the shell's behavior)
Cool, thanks for the numbers.
the 'have 1 vma instead of 32,000 vmas' thing is a really, really big
plus. It makes UML comparable to Xen, in rough terms of basic VM design.
Now imagine a somewhat larger setup - 16 GB RAM UML instance with 4
million vmas per UML process ... Frankly, without
sys_remap_file_pages_prot() the UML design is still somewhat of a toy.
Yes, I guess I imagined the common case might have been slightly better,
however with reasonable RAM utilisation, fragmentation means I wouldn't
be surprised if it does easily get close to that worst theoretical case.
My request for numbers was more about the Intel/glibc people than Paolo:
I do realise it is a problem for UML. I just like to see nice numbers :)
I think UML's really neat, so I'd love to see this get in. I don't see
any fundamental sticking point, given a few iterations, and some more
discussion.
--
SUSE Labs, Novell Inc.
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