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The buffer cache is responsible for managing the holder count, tracking clean/dirty state, and choosing buffers via predicates. Higher level code is responsible for allocation of buffers, IO and eviction/cache sizing. The buffer cache has thread safe methods for acquiring a reference to an existing buffer. All other methods in buffer cache are _not_ threadsafe, and only contain enough locking to guarantee the safe methods. Rather than a single mutex, sharded rw_semaphores are used to allow concurrent threads to 'get' buffers. Each rw_semaphore protects its own rbtree of buffer entries. Code that uses this new dm_buffer_cache abstraction will be introduced in a following commit. This commit moves the dm_buffer struct in preparation for finer grained dm_buffer changes, in the next commit, to be more easily seen. It also introduces temporary dm_buffer struct members to allow compilation of this intermediate commit (they will be elided in the next commit). This commit will cause "defined but not used" compiler warnings that will be resolved by the next commit. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@kernel.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.
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.