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[BACKGROUND] Currently memcpy_extent_buffer() does a loop where it would stop at any page boundary inside [dst_offset, dst_offset + len) or [src_offset, src_offset + len). This is mostly allowing us to do copy_pages(), but if we're going to use folios we will need to handle multi-page (the old behavior) or single folio (the new optimization). The current code would be a burden for future changes. [ENHANCEMENT] There is a hidden pitfall of the naming memcpy_extent_buffer(), unlike regular memcpy(), this function can handle overlapping ranges. So here we extract write_extent_buffer() into a new internal helper, __write_extent_buffer(), and add a new parameter @use_memmove, to indicate whether we should use memmove() or regular memcpy(). Now we can go __write_extent_buffer() to handle writing into the dst range, with proper overlapping detection. This has a tiny change to the chance of calling memmove(). As the split only happens at the source range page boundaries, the memcpy/memmove() range would be slightly larger than the old code, thus slightly increase the chance we call memmove() other than memcopy(). 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 Restructured Text 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.