05f3fb3c53
We currently fully quiesce the ring before an unregister or update of the fixed fileset. This is very expensive, and we can be a bit smarter about this. Add a percpu refcount for the file tables as a whole. Grab a percpu ref when we use a registered file, and put it on completion. This is cheap to do. Upon removal of a file from a set, switch the ref count to atomic mode. When we hit zero ref on the completion side, then we know we can drop the previously registered files. When the old files have been dropped, switch the ref back to percpu mode for normal operation. Since there's a period between doing the update and the kernel being done with it, add a IORING_OP_FILES_UPDATE opcode that can perform the same action. The application knows the update has completed when it gets the CQE for it. Between doing the update and receiving this completion, the application must continue to use the unregistered fd if submitting IO on this particular file. This takes the runtime of test/file-register from liburing from 14s to about 0.7s. Signed-off-by: Jens Axboe <axboe@kernel.dk>
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.