Re: [RFC] perf: mmap2 not covering VM_CLONE regions

[Peter Zijlstra]

On Wed, Oct 02, 2013 at 12:38:54PM -0700, Kees Cook wrote:
> On Wed, Oct 2, 2013 at 12:00 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > On Wed, Oct 02, 2013 at 11:10:15AM -0700, Kees Cook wrote:
> >> Seems like a simple enough solution. Surely there must be a catch. :)
> >
> > I didn't want to add this to the core mm just for perf..
> 
> It seems like it would be pretty inexpensive. It might also be
> valuable in other situations. Not that I can think of any at the
> moment. Additionally, it could likely be hidden by a CONFIG, so that
> if perf isn't built in, there's no change?

You optimist, you think you can build a kernel without perf? ;-)

Its just that I would hate to add more completely global state to the
fork() path. The tasklist_lock might be hard to crack, but at least the
pid-hash could use per bucket locks (it doesn't apparently).

I suppose people don't really care that much about fork() performance;
which is sad. KSM and THP also add their own global locks :-(
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