linux-kernel - Re: Page scan keeps touching kernel text pages

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Message-ID: <20080225151536.GA13358@lazybastard.org>
Date:	Mon, 25 Feb 2008 16:15:36 +0100
From:	Jörn Engel <joern@...fs.org>
To:	Andy Whitcroft <apw@...dowen.org>
Cc:	Jörn Engel <joern@...fs.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: Page scan keeps touching kernel text pages

On Mon, 25 February 2008 15:07:24 +0000, Andy Whitcroft wrote:
> On Sun, Feb 24, 2008 at 03:47:11PM +0100, Jörn Engel wrote:
> > While tracking down some unrelated bug I noticed that shrink_page_list()
> > keeps testing very low page numbers (aka kernel text) until deciding
> > that the page lacks a mapping and cannot get freed.  Looks like a waste
> > of cpu and cachelines to me.
> > 
> > Is there a better reason for this behaviour than lack of a patch?
> 
> shrink_page_list() would be expected to be passed pages pulled from
> the active or inactive lists via isolate_lru_pages()?  I would not have
> expected to find the kernel text on the LRU and therefore not expect to
> see it passed to shrink_page_list()?

Your expectations match mine.  At least someone shares my dilusions. :)

> I would expect to find pages below the kernel text as real pages, and
> potentially on the LRU on some architectures.  Which architecture are
> you seeing this?  Which zones do the pages belong?

32bit x86 (run in qemu, shouldn't make a difference).

Not sure about the zones.  Let me rerun to check that.

Jörn

-- 
Ninety percent of everything is crap.
-- Sturgeon's Law
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