Re: [RFC] Hugetlb demotion for x86

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

On Thu, 2006-05-11 at 16:15 +0100, Hugh Dickins wrote:
> On Wed, 10 May 2006, Adam Litke wrote:
> > 
> > Strict overcommit is there for shared mappings.  When private mapping
> 
> I presume that by "strict overcommit" you mean "strict no overcommit".
> 
> > support was added, people agreed that full overcommit should apply to
> > private mappings for the same reasons normal page overcommit is desired.
> 
> I'm not sure how wide that agreement was.  But what I wanted to say is...
> 
> > For one: an application using lots of private huge pages should not be
> > prohibited from forking if it's likely to just exec a small helper
> > program.
> 
> This is an excellent use for madvise(start, length, MADV_DONTFORK).
> Though it was added mainly for RDMA issues, it's a great way for a
> program with a huge commitment to exclude areas of its address space
> from the fork, so making that fork much more likely to succeed.

I guess it's time for me to take a step back and explain why I am doing
this.  libhugetlbfs (announced here recently) has the ability to remap
an executable's ELF segments into huge pages.  So madvise(MADV_DONTFORK)
would be pretty bad ;)

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