linux-kernel - Re: [PATCH] Add per-process flag to control thp

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Date:	Sun, 04 Aug 2013 14:44:17 +0000
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
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>,
	Mel Gorman <mgorman@...e.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Dave Jones <davej@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Kees Cook <keescook@...omium.org>, Robin Holt <holt@....com>
Subject: Re: [PATCH] Add per-process flag to control thp

Alex Thorlton <athorlton@....com> writes:

> This patch implements functionality to allow processes to disable the use of
> transparent hugepages through the prctl syscall.

A few comments: 

Is there a reason it shouldn't be possible for a process to un-disable/reenable thp? 

> +static inline int transparent_hugepage_enabled(struct vm_area_struct *vma)
> +{
> +	return !current->thp_disabled & _transparent_hugepage_enabled(vma);
> +}

Should probably be &&.

> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 50d04b9..f084c76 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1406,6 +1406,9 @@ struct task_struct {
>  	unsigned int	sequential_io;
>  	unsigned int	sequential_io_avg;
>  #endif
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	int thp_disabled;
> +#endif
>  };

Is there a reason this needs a whole int in task_struct and not just
a single bit?

Rasmus
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