199257a78b
For extent maps, if they are not compressed extents and are adjacent by logical addresses and file offsets, they can be merged into one larger extent map. Such merged extent map will have the higher generation of all the original ones. But this brings a problem for autodefrag, as it relies on accurate extent_map::generation to determine if one extent should be defragged. For merged extent maps, their higher generation can mark some older extents to be defragged while the original extent map doesn't meet the minimal generation threshold. Thus this will cause extra IO. So solve the problem, here we introduce a new flag, EXTENT_FLAG_MERGED, to indicate if the extent map is merged from one or more ems. And for autodefrag, if we find a merged extent map, and its generation meets the generation requirement, we just don't use this one, and go back to defrag_get_extent() to read extent maps from subvolume trees. This could cause more read IO, but should result less defrag data write, so in the long run it should be a win for autodefrag. 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 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.