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When unmapping N pages (e.g. shared memory) the amount of TLB flushes done can be (N*PAGE_SIZE/ZAP_BLOCK_SIZE)*N although it should be N at maximum. With PREEMPT kernel ZAP_BLOCK_SIZE is 8 pages, so there is a noticeable performance penalty when unmapping a large VMA and the system is spending its time in flush_tlb_range(). The problem is that tlb_end_vma() is always flushing the full VMA range. The subrange that needs to be flushed can be calculated by tlb_remove_tlb_entry(). This approach was suggested by Hugh Dickins, and is also used by other arches. The speed increase is roughly 3x for 8M mappings and for larger mappings even more. Signed-off-by: Aaro Koskinen <Aaro.Koskinen@nokia.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> |
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