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Re: ext4dev build failure on mips: "empty_zero_page" undefined

To: Thiemo Seufer <ths@networkno.de>
Subject: Re: ext4dev build failure on mips: "empty_zero_page" undefined
From: Theodore Tso <tytso@mit.edu>
Date: Fri, 6 Jun 2008 09:15:47 -0400
Cc: Vorobiev Dmitri <dmitri.vorobiev@movial.fi>, Martin Michlmayr <tbm@cyrius.com>, Ralf Baechle <ralf@linux-mips.org>, Dmitri Vorobiev <dmitri.vorobiev@gmail.com>, linux-mips@linux-mips.org, linux-ext4@vger.kernel.org
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On Thu, Jun 05, 2008 at 10:51:52PM +0100, Thiemo Seufer wrote:
> > Ted, Ralf seems to be unwilling to accept the ZERO_PAGE() export. If you
> > send the MIPS-specific patch, I can do the testing for you as I have a
> > MIPS Malta board at my disposal.

Ralf sent me a private note saying he would take care of this, but
that he had been very busy with real-world life items.

> AFAIU the problematic case are systems with R4000/R4400 SC/MC CPUs
> since they use 8 zero pages of different color. Have a look at
> arch/mips/mm/init.c:setup_zero_pages.

Right.  So we're not actually going to ever write to the page, but we
are going to add the page to a bio and submit for writing.  I assume
that's not going to cause VECI/VCED exceptions, right?  If the act of
DMA'ing, or worse yet, for older devices/drivers which have to use PIO
to write out a block device is going to cause "thousand and thousands
of exceptions", it sounds like MIPS CPU designers need to be slapped
silly....

                                        - Ted

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