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39cac191ff
Adopt the map ordering to match the other architectures and the generic code. Also make the maximum entries limited and not dependend on the number of CPUs. With the original implementation did the following calculation: nr_slots = mapsize >> PAGE_SHIFT; The results in either 512 or 1024 total slots depending on configuration. The total slots have to be divided by the number of CPUs to get the number of slots per CPU (former KM_TYPE_NR). ARC supports up to 4k CPUs, so this just falls apart in random ways depending on the number of CPUs and the actual kmap (atomic) nesting. The comment in highmem.c: * - fixmap anyhow needs a limited number of mappings. So 2M kvaddr == 256 PTE * slots across NR_CPUS would be more than sufficient (generic code defines * KM_TYPE_NR as 20). is just wrong. KM_TYPE_NR (now KM_MAX_IDX) is the number of slots per CPU because kmap_local/atomic() needs to support nested mappings (thread, softirq, interrupt). While KM_MAX_IDX might be overestimated, the above reasoning is just wrong and clearly the highmem code was never tested with any system with more than a few CPUs. Use the default number of slots and fail the build when it does not fit. Randomly failing at runtime is not a really good option. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Vineet Gupta <vgupta@synopsys.com> Cc: Arnd Bergmann <arnd@arndb.de> Link: https://lore.kernel.org/r/20201103095857.472289952@linutronix.de |
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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.