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

Hillf Danton
2012-08-25T12:47:43Z

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?

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