From: Matthew Wilcox <matthew@wil.cx>
To: Theodore Ts'o <tytso@mit.edu>
Cc: Dave Chinner <david@fromorbit.com>,
Matthew Wilcox <matthew.r.wilcox@intel.com>,
linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 0/3] Add XIP support to ext4
Date: Wed, 18 Dec 2013 21:12:41 -0700 [thread overview]
Message-ID: <20131219041240.GA19166@parisc-linux.org> (raw)
In-Reply-To: <20131219020759.GA27469@thunk.org>
On Wed, Dec 18, 2013 at 09:07:59PM -0500, Theodore Ts'o wrote:
> On Wed, Dec 18, 2013 at 07:27:49AM -0700, Matthew Wilcox wrote:
> >
> > I think there is a callback in xip_file_write(), and it's get_xip_mem().
> > From what you're saying, it sounds like it's just not doing enough.
>
> The problem is that git_xip_mem() is called before we write to the
> memory, right?
>
> We need to convert the uninit extents to be marked as initialized in
> *after* the write has been sent to the storage medium.
Now that I've spent the best part of a day looking at the ext4 code, I
still don't think there's a problem here. With the way the XIP code is
currently written (calling ext4_get_block with create=1), we won't get an
uninitialised extent in the caller. Instead, we'll get one that's been
zeroed (the zeroing is part of patch 3/3 and done only for xip files).
As I understand it, when ext4 uses direct I/O, it can pass
ext4_get_block_write() as the get_block method, which uses the
magic EXT4_GET_BLOCKS_IO_CREATE_EXT flag to permit the allocation of
uninitialised extents. But the regular ext4_get_block cannot create
uninitialised extents (it can return them in the case of create=0,
and we handle that correctly as a hole).
Moreover, I don't see, eg, block_read_full_page() handling uninitialised
extents specially, so I'm pretty sure the regular ext4_get_block()
can't create uninitialised extents.
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
next prev parent reply other threads:[~2013-12-19 4:12 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-17 19:18 [PATCH v3 0/3] Add XIP support to ext4 Matthew Wilcox
2013-12-17 19:18 ` [PATCH v3 1/3] Fix XIP fault vs truncate race Matthew Wilcox
2013-12-17 19:18 ` [PATCH v3 2/3] xip: Add xip_zero_page_range Matthew Wilcox
2013-12-17 19:18 ` [PATCH v3 3/3] ext4: Add XIP functionality Matthew Wilcox
2013-12-17 22:30 ` [PATCH v3 0/3] Add XIP support to ext4 Dave Chinner
2013-12-18 2:31 ` Matthew Wilcox
2013-12-18 5:01 ` Theodore Ts'o
2013-12-18 14:27 ` Matthew Wilcox
2013-12-19 2:07 ` Theodore Ts'o
2013-12-19 4:12 ` Matthew Wilcox [this message]
2013-12-19 4:37 ` Dave Chinner
2013-12-19 5:43 ` Theodore Ts'o
2013-12-19 15:20 ` Matthew Wilcox
2013-12-19 16:17 ` Theodore Ts'o
2013-12-19 17:12 ` Matthew Wilcox
2013-12-19 17:18 ` Theodore Ts'o
2013-12-20 18:17 ` Matthew Wilcox
2013-12-20 19:34 ` Theodore Ts'o
2013-12-20 20:11 ` Matthew Wilcox
2013-12-23 3:36 ` Dave Chinner
2013-12-23 3:45 ` Matthew Wilcox
2013-12-23 4:32 ` Dave Chinner
2013-12-23 6:56 ` Dave Chinner
2013-12-23 14:51 ` Theodore Ts'o
2013-12-23 3:16 ` Dave Chinner
2013-12-24 16:27 ` Matthew Wilcox
2013-12-18 12:33 ` Dave Chinner
2013-12-18 15:22 ` Matthew Wilcox
2013-12-19 0:48 ` Dave Chinner
2013-12-19 1:05 ` Matthew Wilcox
2013-12-19 1:58 ` Dave Chinner
2013-12-19 15:32 ` Matthew Wilcox
2013-12-19 23:46 ` Dave Chinner
2013-12-20 16:45 ` Matthew Wilcox
2013-12-23 4:14 ` Dave Chinner
2013-12-18 18:13 ` Eric Sandeen
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