On KunPeng920 board. When changing permission of a large range region, pmdp_invalidate() takes about 65% in profile (with hugepages) in JIT tool. Kernel will flush tlb twice: first flush happens in pmdp_invalidate, second flush happens at the end of change_protect_range(). The first pmdp_invalidate is not necessary if the hardware support atomic pmdp changing. The atomic changing pimd to zero can prevent the hardware from update asynchronous. So reconstruct it and remove the first pmdp_invalidate. And the second tlb flush can make sure the new tlb entry valid. This patch series add a pmdp_modify_prot transaction abstraction firstly. Then add pmdp_modify_prot_start() in arm64, which uses pmdp_huge_get_and_clear() to atomically fetch the pmd and zero the entry. After rework, the mprotect can get 3~13 times performace gain in range 64M to 512M on KunPeng920: 4K granule/THP on memory size(M) 64 128 256 320 448 512 pre-patch 0.77 1.40 2.64 3.23 4.49 5.10 post-patch 0.20 0.23 0.28 0.31 0.37 0.39 Changes: v2: - fix set_pmd_at compile problems Xuefeng Wang (2): mm: add helpers pmdp_modify_prot_start/commit arm64: mm: rework the pmd protect changing flow arch/arm64/include/asm/pgtable.h | 14 +++++++++++++ include/asm-generic/pgtable.h | 35 ++++++++++++++++++++++++++++++++ mm/huge_memory.c | 19 ++++++++--------- 3 files changed, 57 insertions(+), 11 deletions(-) -- 2.17.1
