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The current implementation of DMABUF memory registration uses a fixed page size for the memory key (mkey), which can lead to suboptimal performance when the underlying memory layout may offer better page size. The optimization improves performance by reducing the number of page table entries required for the mkey, leading to less MTT/KSM descriptors that the HCA must go through to find translations, fewer cache-lines, and shorter UMR work requests on mkey updates such as when re-registering or reusing a cacheable mkey. To ensure safe page size updates, the implementation uses a 5-step process: 1. Make the first X entries non-present, while X is calculated to be minimal according to a large page shift that can be used to cover the MR length. 2. Update the page size to the large supported page size 3. Load the remaining N-X entries according to the (optimized) page shift 4. Update the page size according to the (optimized) page shift 5. Load the first X entries with the correct translations This ensures that at no point is the MR accessible with a partially updated translation table, maintaining correctness and preventing access to stale or inconsistent mappings, such as having an mkey advertising the new page size while some of the underlying page table entries still contain the old page size translations. Signed-off-by: Edward Srouji <edwards@nvidia.com> Reviewed-by: Michael Guralnik <michaelgur@nvidia.com> Link: https://patch.msgid.link/bc05a6b2142c02f96a90635f9a4458ee4bbbf39f.1751979184.git.leon@kernel.org Signed-off-by: Leon Romanovsky <leon@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 reStructuredText 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.