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

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Message-ID: <4DFF8848.2060802@redhat.com>
Date:	Mon, 20 Jun 2011 13:50:00 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Cong Wang <amwang@...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

On 06/20/2011 01:34 PM, Cong Wang wrote:

> Even if it is really 10K, why not save it since it doesn't
> much effort to make this. ;) Not only memory, but also time,
> this could also save a little time to initialize the kernel.
>
> For me, the more serious thing is the logic, there is
> no way to totally disable it as long as I have THP in .config
> currently. This is why I said the design is broken.

There are many things you cannot totally disable as long
as they are enabled in the .config.  Think about things
like swap, or tmpfs - neither of which you are going to
use in the crashdump kernel.

I believe we need to keep the kernel optimized for common
use and convenience.

Crashdump is very much a corner case.  Yes, using less
memory in crashdump is worthwhile, but lets face it -
the big memory user there is likely to be the struct page
array, with everything else down in the noise...
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