Re: [PATCH v5 00/22] Rewrite XIP code and add XIP support to ext4

From: Dave Chinner
Date: Thu Jan 23 2014 - 04:01:45 EST

On Wed, Jan 15, 2014 at 08:24:18PM -0500, Matthew Wilcox wrote:
> This series of patches add support for XIP to ext4. Unfortunately,
> it turns out to be necessary to rewrite the existing XIP support code
> first due to races that are unfixable in the current design.
> Since v4 of this patchset, I've improved the documentation, fixed a
> couple of warnings that a newer version of gcc emitted, and fixed a
> bug where we would read/write the wrong address for I/Os that were not
> aligned to PAGE_SIZE.
> I've dropped the PMD fault patch from this set since there are some
> places where we would need to split a PMD page and there's no way to do
> that right now. In its place, I've added a patch which attempts to add
> support for unwritten extents. I'm still in two minds about this; on the
> one hand, it's clearly a win for reads and writes. On the other hand,
> it adds a lot of complexity, and it probably isn't a win for pagefaults.

I ran this through xfstests, but ext4 in default configuration fails
too many of the tests with filesystem corruption and other cascading
failures on the quick group tests (generic/013, generic/070,
generic/075, generic/091, etc) for me to be able to tell if adding
MOUNT_OPTIONS="-o xip" adds any problems or not....

XIP definitely caused generic/001 to fail, but other than that I
can't really tell. Still, it looks like it functions enough to be
able to add XFS support on top of. I'll get back to you with that ;)


Dave Chinner
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