On Tue, 25 Feb 2014 15:23:35 -0800 (PST) Hugh Dickins [off-list ref] wrote:

On Tue, 25 Feb 2014, Dave Chinner wrote:

quoted

On Tue, Feb 25, 2014 at 02:16:01PM +1100, Stephen Rothwell wrote:

quoted

On Mon, 24 Feb 2014 11:57:10 +1100 Dave Chinner [off-list ref] wrote:

quoted

quoted

Namjae Jeon (10):
  fs: Add new flag(FALLOC_FL_COLLAPSE_RANGE) for fallocate
  xfs: Add support FALLOC_FL_COLLAPSE_RANGE for fallocate

I've pushed these to the following branch:

	git://oss.sgi.com/xfs/xfs.git xfs-collapse-range

And so they'll be in tomorrow's linux-next tree.

quoted

  ext4: Add support FALLOC_FL_COLLAPSE_RANGE for fallocate

I've left this one alone for the ext4 guys to sort out.

So presumably that xfs tree branch is now completely stable and so Ted
could just merge that branch into the ext4 tree as well and put the ext4
part on top of that in his tree.

Well, for some definition of stable. Right now it's just a topic
branch that is merged into the for-next branch, so in theory it is
still just a set of pending changes in a branch in a repo that has
been pushed to linux-next for testing.

That said, I don't see that branch changing unless we find bugs in
the code or a problem with the API needs fixing, at which point I
would add more commits to it and rebase the for-next branch that you
are pulling into the linux-next tree.

Realistically, I'm waiting for Lukas to repost his other pending
fallocate changes (the zero range changes) so I can pull the VFS and
XFS bits of that into the XFS tree and I can test them together
before I'll call the xfs-collapse-range stable and ready to be
merged into some other tree...

...

Emphasis on "might": I expect it's impossible, given your current
approach, but something to be on guard against is unmap_mapping_range()
failing to find and unmap a pte, because the page is mapped at the
"wrong" place in the vma, resulting in BUG_ON(page_mapped(page))
in __delete_from_page_cache().

It should be well tested with non-linear mappings please.  It *should*
be OK, but...

...

FALLOC_FL_COLLAPSE_RANGE: I'm a little sad at the name COLLAPSE,
but probably seven months too late to object.  It surprises me that
you're doing all this work to deflate a part of the file, without
the obvious complementary work to inflate it - presumably all those
advertisers whose ads you're cutting out, will come back to us soon
to ask for inflation, so that they have somewhere to reinsert them ;)

Yes, I was wondering that.  Why not simply "move these blocks from here
to there".


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