[K42-discussion] Large page pinning on K42

[Orran Y Krieger]

Yipkei,

Hmmm, to be frank, I am not sure what would happen if you tried to page 
large pages.  I don't think I explicitly put in anything to disable paging 
for the large pages, but it certainly has never been exercised.  We have 
tended to use large pages for very specialized experiments, and paging 
would never have been kicked off in those experiments.  By the way, in 
defines/paging.H the default option is to emulate how Linux & AIX do 
things, with a fixed pool of large pages allocated up-front.  If you turn 
off that option, large pages are not restricted.  If you want to play in 
this space, it would be great.  I think it would make sense to do it in 
the context of the new chunk allocation that Chris has been putting in. 
The chunk based work is designed to keep memory unfragmented to better 
support large pages.  Basically, memory is handed to a process (or group 
of files) in a large chunk, and then sub-allocated.  That way, when, for 
example, a process goes away, a contigous memory is freed. 

There is no restriction on paging out of large pages, but on the 970 the 
only large page size is 16Meg.  Hence, its pretty darn expensive to page 
it. 
             -- Orran





YipKei Kwok <yipkeikwok at gmail.com> 
Sent by: k42-discussion-bounces+okrieg=us.ibm.com at ozlabs.org
02/17/2006 01:17 PM

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Subject
[K42-discussion] Large page pinning on K42






Hi,

I have several questions regarding paging for large pages on the K42
operating systems.

1. By default, once a large page is allocated, is it pinned in the
memory so it will not be paged out? If no, is there any mechanism
which could enforce such a restriction?

2. Previous research has been done on K42 running on the PowerPC 970FX
(G5) processor. Was paging out of large pages restricted? If yes, is
the restriction imposed by the operating system or the processor?

Thank you very much!

Regards,
Yipkei

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