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When !HIGHMEM, the kmap_local_page() in the scatterlist walker does not actually map anything, and the address it returns is just the address from the kernel's direct map, where each sg entry's data is virtually contiguous. To improve performance, stop unnecessarily clamping data segments to page boundaries in this case. For now, still limit segments to PAGE_SIZE. This is needed to prevent preemption from being disabled for too long when SIMD is used, and to support the alignmask case which still uses a page-sized bounce buffer. Even so, this change still helps a lot in cases where messages cross a page boundary. For example, testing IPsec with AES-GCM on x86_64, the messages are 1424 bytes which is less than PAGE_SIZE, but on the Rx side over a third cross a page boundary. These ended up being processed in three parts, with the middle part going through skcipher_next_slow which uses a 16-byte bounce buffer. That was causing a significant amount of overhead which unnecessarily reduced the performance benefit of the new x86_64 AES-GCM assembly code. This change solves the problem; all these messages now get passed to the assembly code in one part. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
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.