linux-kernel - Re: [RFC patch 3/7] thp: make MADV_HUGEPAGE check for mm->def

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Date:	Mon, 27 Aug 2012 12:39:17 +0200
From:	Gerald Schaefer <gerald.schaefer@...ibm.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	akpm@...ux-foundation.org, aarcange@...hat.com, linux-mm@...ck.org,
	ak@...ux.intel.com, hughd@...gle.com, linux-kernel@...r.kernel.org,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com
Subject: Re: [RFC patch 3/7] thp: make MADV_HUGEPAGE check for mm->def_flags

On Sat, 25 Aug 2012 20:47:37 +0800
Hillf Danton <dhillf@...il.com> wrote:

> On Fri, Aug 24, 2012 at 1:17 AM, Gerald Schaefer
> <gerald.schaefer@...ibm.com> wrote:
> > This adds a check to hugepage_madvise(), to refuse MADV_HUGEPAGE
> > if VM_NOHUGEPAGE is set in mm->def_flags. On System z, the VM_NOHUGEPAGE
> > flag will be set in mm->def_flags for kvm processes, to prevent any
> > future thp mappings. In order to also prevent MADV_HUGEPAGE on such an
> > mm, hugepage_madvise() should check mm->def_flags.
> >
> > Signed-off-by: Gerald Schaefer <gerald.schaefer@...ibm.com>
> > ---
> >  mm/huge_memory.c |    4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1464,6 +1464,8 @@ out:
> >  int hugepage_madvise(struct vm_area_struct *vma,
> >                      unsigned long *vm_flags, int advice)
> >  {
> > +       struct mm_struct *mm = vma->vm_mm;
> > +
> >         switch (advice) {
> >         case MADV_HUGEPAGE:
> >                 /*
> > @@ -1471,6 +1473,8 @@ int hugepage_madvise(struct vm_area_stru
> >                  */
> >                 if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
> >                         return -EINVAL;
> > +               if (mm->def_flags & VM_NOHUGEPAGE)
> > +                       return -EINVAL;
> 
> Looks ifdefinery needed for s390 to wrap the added check, and
> a brief comment?

Hmm, architecture #ifdefs in common code are ugly. I'd rather keep
the check even if it is redundant right now for other architectures
than s390. It is not a performance critical path, and there may be
other users of that in the future.

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