linux-kernel - Re: [PATCH 1/3] mm: completely disable THP by transparent

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Date:	Mon, 20 Jun 2011 12:55:53 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	Amerigo Wang <amwang@...hat.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Johannes Weiner <jweiner@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org
Subject: Re: [PATCH 1/3] mm: completely disable THP by transparent_hugepage=never

On 06/20/2011 12:50 PM, Andrea Arcangeli wrote:
> On Tue, Jun 21, 2011 at 12:34:28AM +0800, Amerigo Wang wrote:
>> transparent_hugepage=never should mean to disable THP completely,
>> otherwise we don't have a way to disable THP completely.
>> The design is broken.
>
> We want to allow people to boot with transparent_hugepage=never but to
> still allow people to enable it later at runtime. Not sure why you
> find it broken... Your patch is just crippling down the feature with
> no gain. There is absolutely no gain to disallow root to enable THP
> later at runtime with sysfs, root can enable it anyway by writing into
> /dev/mem.
>
> Unless you're root and you enable it, it's completely disabled, so I
> don't see what you mean it's not completely disabled. Not even
> khugepaged is started, try to grep of khugepaged...

Agreed, I don't really see the reason for these patches.

Amerigo?
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