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Currently we reject large folios for defrag gracefully, but the
implementation itself is already mostly large folios compatible.
There are several parts of defrag in btrfs:
- Extent map checking
Aka, defrag_collect_targets(), which prepares a list of target ranges
that should be defragged.
This part is completely folio unrelated, thus it doesn't care about
the folio size.
- Target folio preparation
Aka, defrag_prepare_one_folio(), which lock and read (if needed) the
target folio.
Since folio read and lock are already supporting large folios, this
part needs only minor changes.
- Redirty the target range of the folio
This is already done in a way supporting large folios.
So it's pretty straightforward to enable large folios for defrag:
- Do not reject large folios for experimental builds
This affects the large folio check inside defrag_prepare_one_folio().
- Wait for ordered extents of the whole folio in
defrag_prepare_one_folio()
- Lock the whole extent range for all involved folios in
defrag_one_range()
- Allow the folios[] array to be partially empty
Since we can have large folios, folios[] will not always be full.
This affects:
* How to allocate folios in defrag_one_range()
Now we cannot use page index, but use the end position of the folio
as an iterator.
* How to free the folios[] array
If we hit an empty slot, it means we have large folios and already
hit the end of the array.
* How to mark the range dirty
Instead of use page index directly, we have to go through each
folio, and check if the folio covers the defrag target inside
defrag_one_locked_target().
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.