[haiku] Re: Fwd: x86_64 build failed with gcc4 based x86_64 linux distros
- From: François Revol <revol@xxxxxxx>
- To: haiku@xxxxxxxxxxxxx
- Date: Thu, 28 Jul 2011 00:29:28 +0200
Le mercredi 27 juillet 2011 à 22:56 +0200, Ingo Weinhold a écrit :
> François Revol wrote:
> > Le mercredi 27 juillet 2011 à 17:44 +0200, Stephan Assmus a écrit :
> > > That being said, I believe the point of implementing PAE support (yes it
> > > exists) was to be able to address more than 4 GB. Each individual
> > > process in Haiku can only address 4GB, but the kernel should be able to
> > > use more than 4GB for the mapping of virtual to physical memory. That is
> >
> > Yep, the PAE paging code uses 64bit types to hold the physical
> > addresses, which seems to be 40bit according to the bitmasks in paging.h
>
> The actually supported physical address width is processor dependent. The
> maximum possible width is 52 bit (4 PiB). That's the same for x86_64.
Oh right, the 40bits are the page addresses, +12bits for offsets in the
page.
> > > of course only interesting when more than one process is running at a
> > > time, and affects the necessity for swapping out pages. For example,
> > > when one process indeed uses all of it's 4GB address space, the Haiku
> > > kernel does not necessarily need to swap out virtual memory, when there
> > > are more then 4GB available in physical RAM, since the address space of
> > > another process could be mapped to another range of the physical memory.
> > > Hope I have remembered these details correctly.
>
> More interestingly even, the kernel directly uses physical memory for the
> file cache (unfortunately not for the block cache yet). So one can still
> benefit from more installed RAM even when not using memory hungry
> applications.
And RAM disks, ...
François.
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