Re: [PATCH] hugetlb: powerpc: Actively close unused htlb regions on vma close

[Adam Litke <agl@us.ibm.com>]

On Fri, 2006-06-02 at 17:43 +0100, Hugh Dickins wrote:
> On Fri, 2 Jun 2006, Adam Litke wrote:
> > 
> > On powerpc, each segment can contain pages of only one size.  When a
> > hugetlb mapping is requested, a segment is located and marked for use
> > with huge pages.  This is a uni-directional operation -- hugetlb
> > segments are never marked for use again with normal pages.  For long
> > running processes which make use of a combination of normal and hugetlb
> > mappings, this behavior can unduly constrain the virtual address space.
> > 
> > The following patch introduces a architecture-specific vm_ops.close()
> > hook.  For all architectures besides powerpc, this is a no-op.  On
> > powerpc, the low and high segments are scanned to locate empty hugetlb
> > segments which can be made available for normal mappings.  Comments?
> 
> Wouldn't hugetlb_free_pgd_range be a better place to do that kind of
> thing, all within arch/powerpc, no need for arch_hugetlb_close_vma etc?

Hmm.  Interesting idea.  I'll take a look.

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center