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

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Message-ID: <4DFF7CDD.308@redhat.com>
Date:	Tue, 21 Jun 2011 01:01:17 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Rik van Riel <riel@...hat.com>,
	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

于 2011年06月21日 00:50, Andrea Arcangeli 写道:
> 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.


What can I do if I don't want to see THP at all? I mean the same
behavior as when my CPU doesn't have PSE.

With this patch, there is no even /sys/kernel/vm/transparent_hugepage/
exists.

>
> 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... (that wouldn't be
> the same with ksm where ksm daemon runs even when it's off for no
> gain, but I explicitly solved the locking so khugepaged will go away
> when enabled=never and return when enabled=always).

Without this patch, THP is still initialized (although khugepaged is not started),
that is what I don't want to see when I pass "transparent_hugepage=never",
because "never" for me means THP is totally unseen, even not initialized.

Thanks.
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