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

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Message-ID: <20140123090133.GR13997@dastard>
Date:	Thu, 23 Jan 2014 20:01:34 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v5 00/22] Rewrite XIP code and add XIP support to ext4

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 ;)

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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