Re: [PATCH] Add per-process flag to control thp

From: Oleg Nesterov
Date: Sun Aug 04 2013 - 10:25:52 EST

On 08/03, Kees Cook wrote:
> On Fri, Aug 2, 2013 at 1:34 PM, Alex Thorlton <athorlton@xxxxxxx> wrote:
> >
> >> And I think thp_disabled should be reset to 0 on exec.
> >
> > The main purpose for this getting carried down from the parent process
> > is that we'd like to be able to have a userland program set this flag on
> > itself, and then spawn off children who will also carry the flag.
> > This allows us to set the flag for programs where we're unable to modify
> > the code, thus resolving the issues detailed above.
> This could be done with LD_PRELOAD for uncontrolled binaries. Though
> it does seem sensible to make it act like most personality flags do
> (i.e. inherited).

It is only inheritable if the process is single-threaded.

And even if it is single-threaded I can't understand how it can really

OK, transparent_hugepage_enabled() checks ->thp_disabled, but this is
the fault path. But this flag can't hide the task from khugepaged and
collapse_huge_page ?

I still think this should be mm flag. And we have MMF_INIT_MASK, it
can be inheritable.


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