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When there are no ongoing transactions and the log contents have been checkpointed back into the filesystem, the log performs 'covering', which is to say that it log a dummy transaction to record the fact that the tail has caught up with the head. This is a good time to clear log incompat feature flags, because they are flags that are temporarily set to limit the range of kernels that can replay a dirty log. Since it's possible that some other higher level thread is about to start logging items protected by a log incompat flag, we create a rwsem so that upper level threads can coordinate this with the log. It would probably be more performant to use a percpu rwsem, but the ability to /try/ taking the write lock during covering is critical, and percpu rwsems do not provide that. Signed-off-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Allison Henderson <allison.henderson@oracle.com> Reviewed-by: Chandan Babu R <chandanrlinux@gmail.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.