Re: [RFC PATCHv2 1/2] Add mm flag to control THP

[Andy Lutomirski]

On Thu, Jan 16, 2014 at 1:01 PM, Alex Thorlton <athorlton@xxxxxxx> wrote:
> This patch adds an mm flag (MMF_THP_DISABLE) to disable transparent
> hugepages using prctl.
>

> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1998,6 +1998,17 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>                 if (arg2 || arg3 || arg4 || arg5)
>                         return -EINVAL;
>                 return current->no_new_privs ? 1 : 0;
> +       case PR_SET_THP_DISABLE:
> +               if (arg2)
> +                       set_bit(MMF_THP_DISABLE, &me->mm->flags);
> +               else
> +                       clear_bit(MMF_THP_DISABLE, &me->mm->flags);
> +               break;
> +       case PR_GET_THP_DISABLE:
> +               error = put_user(test_bit(MMF_THP_DISABLE,
> +                                &me->mm->flags),
> +                                (int __user *) arg2);
> +               break;

Usual nit: please return -EINVAL if unused args are nonzero.  This
makes it possible to extend these APIs in the future.

--Andy
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