Re: Pagecache: find_or_create_page does not call a proper pageallocator function
From: Andrew Morton
Date: Tue Apr 24 2007 - 16:11:55 EST
On Tue, 24 Apr 2007 12:59:17 -0700 (PDT) Christoph Lameter <clameter@xxxxxxx> wrote:
> 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???
yep. Take a 4k page which is stored in four discontiguous 1k disk blocks. The
data at page_buffers(page) is the sole way in which we track which parts of
the page belong to which blocks of the disk.
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