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

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Message-ID: <CALCETrVO+gr2aeDzOz2x8kWKBDG04ugb2GjWdPphUsNzACKzoA@mail.gmail.com>
Date:	Fri, 17 Jan 2014 11:54:09 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Alex Thorlton <athorlton@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rik van Riel <riel@...hat.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Kees Cook <keescook@...omium.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC PATCHv2 1/2] Add mm flag to control THP

On Thu, Jan 16, 2014 at 1:01 PM, Alex Thorlton <athorlton@....com> 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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