linux-kernel - Re: [RFC] i386: Remove page sized slabs for pgds and pmds

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Message-Id: <20070328134511.0d61ec8f.akpm@linux-foundation.org>
Date:	Wed, 28 Mar 2007 13:45:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	linux-kernel@...r.kernel.org,
	William Lee Irwin III <wli@...omorphy.com>
Subject: Re: [RFC] i386: Remove page sized slabs for pgds and pmds

On Wed, 28 Mar 2007 13:12:56 -0700 (PDT)
Christoph Lameter <clameter@....com> wrote:

> The benefit of preconstructed pgds and pmds in the i386 arch code seem to
> be debatable. The performance measurements indicate that there may be a slight
> benefit but it seems to almost vanish in the noise ratio.

yeah, I did a couple hours testing with rc5, rc5+quicklists,
rc5+quicklists+qlhack, where "qlhack" is my patch which removes the
quicklists and mysteriously causes i386 to crash.

I was testing 8-way x86_64 with patch-scripts (wildly fork-intensive),
kernel build and lmbench.

Basically I was unable to observe any statistically meaningful-looking
differences between any of them.

I would like to test qlhack on ia64, because ia64 puts pte-pages into the
quicklists as well, but my ia64 machine is presently indisposed.

My (much) preferred way to handle all this is to remove the quicklists from
all architectures: just use alloc_page() and free_page() for pte pages, pmd
pages, etc.  I remain unaware of any testing whcih indicates that this
would be a bad change.

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