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SubjectRe: [RFC] Hugetlb demotion for x86
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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

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