Subject: Re: 4MB pages?
To: Matt Thomas <>
From: Jason R Thorpe <>
List: tech-kern
Date: 09/06/2000 09:38:22
On Wed, Sep 06, 2000 at 08:16:42AM -0700, Matt Thomas wrote:

 > For memory intensive (mmap large files, etc.) programs, I was wondering whether
 > it would be useful to have another uvm free page area which contains free 4MB
 > blocks.  As memory gets freed, as a complete 4MB block is freed it would be
 > moved to the free 4MB list.

That's possible... I haven't really looked at that, yet.

 > 4MB page table entries would be real useful for mapping framebuffers as 
 > well but
 > that requires a[nother] change to the driver mmap interface.

Yes, I agree.  I'd like to introduce a pmap_enter_range() and a set of
macros that UVM can use to properly align the address, etc.  That's a
ways off yet, tho.  In particular, dealing w/ e.g. PV entries is going
to be tricky.  At first, limiting it to unmanaged pages (like e.g. frame
buffers, or memory that has been stolen to be managed by something else,
like, say, pools) seems reasonable.

 > Note that these idea are applicable to other architectures that support 
 > superpages
 > such as alpha.

        -- Jason R. Thorpe <>