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Re: [patch 00/14] remap_file_pages protection support

From:  Ingo Molnar <>
To:  Nick Piggin <>
Subject:  Re: [patch 00/14] remap_file_pages protection support
Date:  Tue, 2 May 2006 13:24:09 +0200
Cc:, Andrew Morton <>,, Linux Memory Management <>
Archive-link:  Article, Thread

* Nick Piggin <> wrote:

> >Let's try get back to the good old days when people actually reported
> >their bugs (togther will *real* numbers) to the mailing lists. That way,
> >everybody gets to think about and discuss the problem.
> Speaking of which, let's see some numbers for UML -- performance and 
> memory. I don't doubt your claims, but I (and others) would be 
> interested to see.

firstly, thanks for the review feedback!

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)

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.


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