linux-kernel - Re: Pagecache: find_or_create_page does not call a proper page allocator function

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Message-ID: <Pine.LNX.4.64.0704241256470.12907@schroedinger.engr.sgi.com>
Date:	Tue, 24 Apr 2007 12:59:17 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Hugh Dickins <hugh@...itas.com>, Nick Piggin <npiggin@...e.de>,
	linux-kernel@...r.kernel.org, pj@....com
Subject: Re: Pagecache: find_or_create_page does not call a proper page
 allocator function

On Tue, 24 Apr 2007, Andrew Morton wrote:

> No, think of the following scenario:
> 
> - file I/O causes a read of an ext2 file's bitmap.  The bitmap is
>   brought into /dev/hda1's pagecache using !__GFP_HIGHMEM
> 
> - references are released against that page and it's now just clean
>   reclaimable pagecache
> 
> - someone (say, an online filesystem checker or something) mmaps
>   /dev/hda1 and reads that page.
> 
> - migration comes alnog and migrates that page into highmem
> 
> - file I/O causes a read of that bitmap again.  We find it in
>   /dev/hda's pagecache.

Read of the bitmap? How would that work? Page cache lookup right?

>   Here's set_bh_page().

A highmem page can have buffers???
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