linux-kernel - Re: [PATCHv2] Add per-process flag to control thp

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Date:	Sat, 3 Aug 2013 19:01:02 +0200
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>,
	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>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Kees Cook <keescook@...omium.org>, Robin Holt <holt@....com>
Subject: Re: [PATCHv2] Add per-process flag to control thp

On 08/02, Alex Thorlton wrote:
>
> This patch implements functionality to allow processes to disable the use of
> transparent hugepages through the prctl syscall.
>
> We've determined that some jobs perform significantly better with thp disabled,
> and we needed a way to control thp on a per-process basis, without relying on
> madvise.

Well, I think the changelog should explain why madvise() is bad.

> @@ -1311,6 +1311,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  	p->sequential_io_avg	= 0;
>  #endif
>
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	p->thp_disabled = current->thp_disabled;
> +#endif

Unneeded. It will be copied by dup_task_struct() automagically.

But I simply can't understand why this flag is per-thread. It should be
mm flag, no?

Oleg

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