Commit 742f3c81 authored Dec 07, 2018 by Anton Ivanov Committed by Richard Weinberger Dec 27, 2018

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 <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

parent 8892d854

arch/um/kernel/tlb.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -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))
		if (pte_present(*pte)) {
		if (pte_newpage(*pte))
		ret = add_mmap(addr, pte_val(*pte) & PAGE_MASK,
		PAGE_SIZE, prot, hvc);
		else
		} else
		ret = add_munmap(addr, PAGE_SIZE, hvc);
		} else if (pte_newprot(*pte))
		ret = add_mprotect(addr, PAGE_SIZE, prot, hvc);