linux-kernel - Re: [RFC PATCHv2 2/2] Change khugepaged to respect MMF_THP

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Date:	Sun, 19 Jan 2014 01:49:57 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Alex Thorlton <athorlton@....com>
Cc:	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>,
	Andy Lutomirski <luto@...capital.net>,
	Al Viro <viro@...iv.linux.org.uk>,
	Kees Cook <keescook@...omium.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC PATCHv2 2/2] Change khugepaged to respect MMF_THP_DISABLE
 flag

On Thu, Jan 16, 2014 at 03:01:44PM -0600, Alex Thorlton wrote:
> This just adds a simple check to get khugepaged to behave
> appropriately when MMF_THP_DISABLE is set.
> 
> Signed-off-by: Alex Thorlton <athorlton@....com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: linux-kernel@...r.kernel.org
> 
> ---
>  mm/huge_memory.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 9c0b172..3cfe6b4 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2049,7 +2049,8 @@ static void insert_to_mm_slots_hash(struct mm_struct *mm,
>  
>  static inline int khugepaged_test_exit(struct mm_struct *mm)
>  {
> -	return atomic_read(&mm->mm_users) == 0;
> +	return atomic_read(&mm->mm_users) == 0 ||
> +	       (mm->flags & MMF_THP_DISABLE_MASK);

__khugepaged_enter() has VM_BUG_ON(khugepaged_test_exit(mm)).
Do we really want to crash there if MMF_THP_DISABLE is set?

-- 
 Kirill A. Shutemov
--
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