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Currently for radix, flush_tlb_range flushes the entire PID, because the Linux mm code does not tell us about page size here for THP vs regular pages. This is quite sub-optimal for small mremap / mprotect / change_protection. So implement va range flushes with two flush passes, one for each page size (regular and THP). The second flush has an order of matnitude fewer tlbie instructions than the first, so it is a relatively small additional cost. There is still room for improvement here with some changes to generic APIs, particularly if there are mostly THP pages to be invalidated, the small page flushes could be reduced. Time to mprotect 1 page of memory (after mmap, touch): vanilla 2.9us 1.8us patched 1.2us 1.6us Time to mprotect 30 pages of memory (after mmap, touch): vanilla 8.2us 7.2us patched 6.9us 17.9us Time to mprotect 34 pages of memory (after mmap, touch): vanilla 9.1us 8.0us patched 9.0us 8.0us 34 pages is the point at which the invalidation switches from va to entire PID, which tlbie can do in a single instruction. This is why in the case of 30 pages, the new code runs slower for this test. This is a deliberate tradeoff already present in the unmap and THP promotion code, the idea is that the benefit from avoiding flushing entire TLB for this PID on all threads in the system. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
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| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.