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The address space flag AS_STABLE_WRITES determine if FGP_STABLE for will wait for the folio to finish its writeback. For btrfs, due to the default data checksum behavior, if we modify the folio while it's still under writeback, it will cause data checksum mismatch. Thus for quite some call sites we manually call folio_wait_writeback() to prevent such problem from happening. Currently there is only one call site inside btrfs really utilizing FGP_STABLE, and in that case we also manually call folio_wait_writeback() to do the waiting. But it's better to properly expose the stable writes flag to a per-inode basis, to allow call sites to fully benefit from FGP_STABLE flag. E.g. for inodes with NODATASUM allowing beginning dirtying the page without waiting for writeback. This involves: - Update the mapping's stable write flag when setting/clearing NODATASUM inode flag using ioctl This only works for empty files, so it should be fine. - Update the mapping's stable write flag when reading an inode from disk - Remove the explicit folio_wait_writeback() for FGP_BEGINWRITE call site Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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.