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Date: Tue, 11 Oct 2011 12:36:05 -0500
From: Mark Tinguely <marktinguely@gmail.com>
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To: Alan Cox <alc@rice.edu>
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Cc: alc@freebsd.org, Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>,
	Kostik Belousov <kostikbel@gmail.com>, hackers@freebsd.org,
	Grzegorz Kulewski <grzegorz@kulewski.pl>
Subject: Re: mmap performance and memory use
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On 10/11/2011 11:12 AM, Alan Cox wrote:
> On 10/10/2011 16:28, Wojciech Puchar wrote:
>> is it possible to force VM subsystem to operate on superpages when 
>> possible - i mean swapping in 2MB chunks?
>>
>
> Currently, no.  For some applications, like the Sun/Oracle JVM, that 
> have code to explicitly manage large pages, there could be some 
> benefit in the form of reduced overhead.  So, it's on my "to do" list, 
> but no where near the top of that list.
>
> Alan
>

Am I correct in remembering that super-pages have to be aligned on the 
super-page boundary and be contiguous?

If so, in the mmap(), he may want to include the 'MAP_FIXED' flag with 
an address that is on a super-page boundary. Right now, the 
"VMFS_ALIGNED_SPACE" that does the VA super-page alignment is only used 
for device pagers.

Similarly, if the allocated physical pages for the object are not 
contiguous, then MAP_PREFAULT_READ will not result in a super-page 
promotion.

--Mark Tinguely