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commitdc7292a5bcupstream. In 'commit752f66a75a("bcache: use REQ_PRIO to indicate bio for metadata")' REQ_META is replaced by REQ_PRIO to indicate metadata bio. This assumption is not always correct, e.g. XFS uses REQ_META to mark metadata bio other than REQ_PRIO. This is why Nix noticed that bcache does not cache metadata for XFS after the above commit. Thanks to Dave Chinner, he explains the difference between REQ_META and REQ_PRIO from view of file system developer. Here I quote part of his explanation from mailing list, REQ_META is used for metadata. REQ_PRIO is used to communicate to the lower layers that the submitter considers this IO to be more important that non REQ_PRIO IO and so dispatch should be expedited. IOWs, if the filesystem considers metadata IO to be more important that user data IO, then it will use REQ_PRIO | REQ_META rather than just REQ_META. Then it seems bios with REQ_META or REQ_PRIO should both be cached for performance optimation, because they are all probably low I/O latency demand by upper layer (e.g. file system). So in this patch, when we want to decide whether to bypass the cache, REQ_META and REQ_PRIO are both checked. Then both metadata and high priority I/O requests will be handled properly. Reported-by: Nix <nix@esperi.org.uk> Signed-off-by: Coly Li <colyli@suse.de> Reviewed-by: Andre Noll <maan@tuebingen.mpg.de> Tested-by: Nix <nix@esperi.org.uk> Cc: stable@vger.kernel.org Cc: Dave Chinner <david@fromorbit.com> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.