linux-kernel - Re: [PATCH 2/3] mm: make the threshold of enabling THP configurable

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Message-ID: <4E01E148.2080302@redhat.com>
Date:	Wed, 22 Jun 2011 20:34:16 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Andrea Arcangeli <aarcange@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org
Subject: Re: [PATCH 2/3] mm: make the threshold of enabling THP configurable

于 2011年06月22日 19:15, Mel Gorman 写道:
> On Wed, Jun 22, 2011 at 06:46:39PM +0800, Cong Wang wrote:
>> ??? 2011???06???22??? 17:16, Mel Gorman ??????:
>>>
>>> What I meant was that there is a rational reason why 512M is the
>>> default for enabling THP by default. Tuning it lower than that by any
>>> means makes very little sense. Tuning it higher might make some sense
>>> but it is more likely that THP would simply be disabled via sysctl. I
>>> see very little advantage to introducing this Kconfig option other
>>> than as a source of confusion when running make oldconfig.
>>>
>>
>> The tunable range is (512, 8192), so 512M is the minimum.
>>
>> Sure, I knew it can be disabled via /sys, actually we can do even
>> more in user-space, that is totally move the 512M check out of kernel,
>> why we didn't?
>>
>
> Because the reason why 512M is the default is not obvious and there
> was no guarantee all distros would chose a reasonable default for
> an init script (or know that an init script was even necessary).
> This is one of the few cases where there is a sensible default that
> is the least surprising.
>

Putting a well-explained Kconfig help would solve this problem,
so I don't think this is a surprising thing.
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