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

[Hillf Danton]

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

>                 *vm_flags &= ~VM_NOHUGEPAGE;
>                 *vm_flags |= VM_HUGEPAGE;
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