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

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Date:	Fri, 17 Jan 2014 21:34:44 +0100
From:	Oleg Nesterov <oleg@...hat.com>
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>,
	"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 01/16, Alex Thorlton wrote:
>
>  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);
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

test_bit(MMF_THP_DISABLE) ?

And I am not sure this and another check in transparent_hugepage_enabled
is actually right...

I think that MMF_THP_DISABLE_MASK should not disable thp if this
vma has VM_HUGEPAGE set, iow perhaps madvise() should work even
after PR_SET_THP_DISABLE?

IOW, MMF_THP_DISABLE should act as khugepaged_req_madv().

But again, I won't argue.

Oleg.

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