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

Gerald Schaefer
2012-08-27T10:39:26Z

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

> On Fri, Aug 24, 2012 at 1:17 AM, Gerald Schaefer
> <gerald.schaefer@de.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@de.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.