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

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Message-ID: <4E0159E9.10800@redhat.com>
Date:	Wed, 22 Jun 2011 10:56:41 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	Vivek Goyal <vgoyal@...hat.com>, Rik van Riel <riel@...hat.com>,
	Mel Gorman <mgorman@...e.de>, 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

于 2011年06月21日 22:43, Andrea Arcangeli 写道:
> On Tue, Jun 21, 2011 at 12:08:14PM +0800, Cong Wang wrote:
>> The thing is that we can save ~10K by adding 3 lines of code as this
>> patch showed, where else in kernel can you save 10K by 3 lines of code?
>> (except some kfree() cases, of course) So, again, why not have it? ;)
>
> Because you could save it with a more complicated patch that doesn't
> cripple down functionality.


Why do you prefer "more complicated" things to simple ones? ;-)

I realized this patch changed the original behavior of "=never",
thus proposed a new "=0" parameter.

But to be honest, "=never" should be renamed to "=disable".

> Again if you want to optimize this ~8KB gain, I recommend to add a
> param to make the hash size dynamic not to prevent the feature to ever
> be enabled again, so by making the code more complex at least it will
> also be useful if we want to increase the size hash at boot time (not
> only to decrease it).
>

Not only such things, the more serious thing is that you are
enforcing a policy to users, as long as I enable THP in Kconfig,
I have no way to disable it.

Why are you so sure that every user who has no chance to change
.config likes THP?

And, what can I do if I want to prevent any process from having
a chance to enable THP? Because as long as THP exists in /sys,
any process has the right privilege can change it.

Thanks.
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