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560507cbc1Brian Foster <bfoster@redhat.com> says: This adds folio batch support for iomap. This initially only targets zero range, the use case being zeroing of dirty folios over unwritten mappings. There is potential to support other operations in the future: iomap seek data/hole has similar raciness issues as zero range, the prospect of using this for buffered write has been raised for granular locking purposes, etc. The one major caveat with this zero range implementation is that it doesn't look at iomap_folio_state to determine whether to zero a sub-folio portion of the folio. Instead it just relies on whether the folio was dirty or not. This means that spurious zeroing of unwritten ranges is possible if a folio is dirty but the target range includes a subrange that is not. The reasoning is that this is essentially a complexity tradeoff. The current use cases for iomap_zero_range() are limited mostly to partial block zeroing scenarios. It's relatively harmless to zero an unwritten block (i.e. not a correctness issue), and this is something that filesystems have done in the past without much notice or issue. The advantage is less code and this makes it a little easier to use a filemap lookup function for the batch rather than open coding more logic in iomap. That said, this can probably be enhanced to look at ifs in the future if the use case expands and/or other operations justify it. WRT testing, I've tested with and without a local hack to redirect fallocate zero range calls to iomap_zero_range() in XFS. This helps test beyond the partial block/folio use case, i.e. to cover boundary conditions like full folio batch handling, etc. I recently added patch 7 in spirit of that, which turns this logic into an XFS errortag. Further comments on that are inline with patch 7. * patches from https://lore.kernel.org/20251003134642.604736-1-bfoster@redhat.com: xfs: error tag to force zeroing on debug kernels iomap: remove old partial eof zeroing optimization xfs: fill dirty folios on zero range of unwritten mappings xfs: always trim mapping to requested range for zero range iomap: optional zero range dirty folio processing iomap: remove pos+len BUG_ON() to after folio lookup filemap: add helper to look up dirty folios in a range Signed-off-by: Christian Brauner <brauner@kernel.org> |
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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.