From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Alex Thorlton <athorlton@sgi.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Dave Jones <davej@redhat.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        David Howells <dhowells@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Al Viro <viro@zeniv.linux.org.uk>, Oleg Nesterov <oleg@redhat.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Kees Cook <keescook@chromium.org>, Robin Holt <holt@sgi.com>
Subject: Re: [PATCH] Add per-process flag to control thp
Organization: D03
References: <20130802194659.GP26476@sgi.com>
Date: Sun, 04 Aug 2013 14:44:17 +0000
In-Reply-To: <20130802194659.GP26476@sgi.com> (Alex Thorlton's message of
	"Fri, 2 Aug 2013 14:46:59 -0500")
Message-ID: <878v0hplby.fsf@rasmusvillemoes.dk>
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Alex Thorlton <athorlton@sgi.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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