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

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Date:	Tue, 21 Jun 2011 01:19:02 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Rik van Riel <riel@...hat.com>
CC:	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Andrea Arcangeli <aarcange@...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 01:10, Rik van Riel 写道:
> On 06/20/2011 01:07 PM, Cong Wang wrote:
>> 于 2011年06月21日 00:58, Mel Gorman 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.
>>>>
>>>
>>> I don't get why it's broken. Why would the user be prevented from
>>> enabling it at runtime?
>>>
>>
>> We need to a way to totally disable it, right? Otherwise, when I configure
>> THP in .config, I always have THP initialized even when I pass "=never".
>>
>> For me, if you don't provide such way to disable it, it is not flexible.
>>
>> I meet this problem when I try to disable THP in kdump kernel, there is
>> no user of THP in kdump kernel, THP is a waste for kdump kernel. This is
>> why I need to find a way to totally disable it.
>
> What you have not explained yet is why having THP
> halfway initialized (but not used, and without a
> khugepaged thread) is a problem at all.
>
> Why is it a problem for you?

It occupies some memory, memory is valuable in kdump kernel (usually
only 128M). :) Since I am sure no one will use it, why do I still need
to initialize it at all?

Thanks.
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