From 742f3c8193a3cb3e444887211214ef0721e3ef8d Mon Sep 17 00:00:00 2001 From: Anton Ivanov Date: Fri, 7 Dec 2018 09:05:53 +0000 Subject: [PATCH] um: Optimize Flush TLB for force/fork case When UML handles a fork the page tables need to be brought up to date. That was done using brute force - full tlb flush. This is actually unnecessary, because the mapped-in mappings are all correct and the only mappings which need to be updated after a flush are any unmaps (so that paging works) as well as any pending protection changes. This optimization squeezes out up to 3% from a full kernel rebuild time under memory pressure. Signed-off-by: Anton Ivanov Signed-off-by: Richard Weinberger --- arch/um/kernel/tlb.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c index 9ca902df243a..8347161c2ae0 100644 --- a/arch/um/kernel/tlb.c +++ b/arch/um/kernel/tlb.c @@ -242,10 +242,11 @@ static inline int update_pte_range(pmd_t *pmd, unsigned long addr, prot = ((r ? UM_PROT_READ : 0) | (w ? UM_PROT_WRITE : 0) | (x ? UM_PROT_EXEC : 0)); if (hvc->force || pte_newpage(*pte)) { - if (pte_present(*pte)) - ret = add_mmap(addr, pte_val(*pte) & PAGE_MASK, - PAGE_SIZE, prot, hvc); - else + if (pte_present(*pte)) { + if (pte_newpage(*pte)) + ret = add_mmap(addr, pte_val(*pte) & PAGE_MASK, + PAGE_SIZE, prot, hvc); + } else ret = add_munmap(addr, PAGE_SIZE, hvc); } else if (pte_newprot(*pte)) ret = add_mprotect(addr, PAGE_SIZE, prot, hvc);