Message-ID: <4E0159E9.10800@redhat.com>
Date: Wed, 22 Jun 2011 10:56:41 +0800
From: Cong Wang <amwang@redhat.com>
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To: Andrea Arcangeli <aarcange@redhat.com>
CC: Vivek Goyal <vgoyal@redhat.com>, Rik van Riel <riel@redhat.com>,
        Mel Gorman <mgorman@suse.de>, linux-kernel@vger.kernel.org,
        akpm@linux-foundation.org, Johannes Weiner <jweiner@redhat.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, linux-mm@kvack.org
Subject: Re: [PATCH 1/3] mm: completely disable THP by transparent_hugepage=never
References: <20110620165844.GA9396@suse.de> <4DFF7E3B.1040404@redhat.com> <4DFF7F0A.8090604@redhat.com> <4DFF8106.8090702@redhat.com> <4DFF8327.1090203@redhat.com> <4DFF84BB.3050209@redhat.com> <4DFF8848.2060802@redhat.com> <20110620182558.GF4749@redhat.com> <20110620192117.GG20843@redhat.com> <4E00192E.70901@redhat.com> <20110621144346.GQ20843@redhat.com>
In-Reply-To: <20110621144346.GQ20843@redhat.com>
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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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