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b2e743927f
Currently if btrfs has its block size (the older sector size) smaller than the page size, btrfs_do_readpage() will handle the range extent by extent, this is good for performance as it doesn't need to re-lookup the same extent map again and again. (Although get_extent_map() already does extra cached em check, thus the optimization is not that obvious.) This is totally fine and is a valid optimization, but it has an assumption that there is no partial uptodate range in the page. Meanwhile there is an incoming feature, requiring btrfs to skip the full page read if a buffered write range covers a full block but not a full page. In that case, we can have a page that is partially uptodate, and the current per-extent lookup cannot handle such case. So here we change btrfs_do_readpage() to do block-by-block read, this simplifies the following things: - Remove the need for @iosize variable Because we just use sectorsize as our increment. - Remove @pg_offset, and calculate it inside the loop when needed It's just offset_in_folio(). - Use a for() loop instead of a while() loop This will slightly reduce the read performance for subpage cases, but for the future where we need to skip already uptodate blocks, it should still be worth. For block size == page size, this brings no performance change. Reviewed-by: Filipe Manana <fdmanana@suse.com> 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.